The Invisible Enemy

[King Kurt]

I have posted my thoughts direct to Franc - but basically attack with escorts - we can't use the Martlets as it is night.

[ELITEofWARMANGINGERYBREADMEN88]

I say lets go hunting!!

[Napoleon The Emperor Of Europe]

Yo.

[Franconicus]

Chapter 5 – 15. December

Walker hesitates a moment, but then he realizes the threat that hides there about three nautical miles on the right. If there is really a submarine, it located the convoy and will soon call the other submarines. There is no alternative, this submarine has to found and eliminated or the convoy will soon get into troubled waters.
The Stork, the destroyer Exmoor and the corvette Convulvulus turn right and hurry to reach the place where the Swodfish dropped its bombs. In the meantime the convoy turns southwest, to get away from the submarine.
Now the search begins. Walker’s Stork is front runner then slows down to listen while other ships approach on either side. In his mind Walker marks a circle around the assumed position of the submarine. The three ships are ploughing the waters with their ASDICs inside this circle. All the time the men have the strange feeling that the submarine is watching them, maybe just adjusting the launching tubes to send them to the deepness.
The search inside the circle takes almost an hour, but there is no contact. Walker feels pain in the stomach, maybe because of something the ate, maybe because he knows that the escort of the convoy is weak and the submarine could attack, right now, while he was wasting his time on the search. On the other hand, it could still be here. If so, he has to find it. He sends signals to the other ships and soon all three lay silently, just watching and listening. Maybe the commander of the submarine things that the search is over and comes to the surface. Then he will get a bad surprise. However, he could also try to attack the British ships, which are perfect targets now. Nothing happens at all. And maybe this is the worst thing for the nerves of the British sailors. Finally, Walker decides to give up the search and to return to the convoy. At four o’clock in the morning he arrives. Fortunately, everything is alright. The three escort ships take their positions. The convoy still sails course southwest, now leaving grid square CG97 and entering DJ21. Behind the ships the sun rises. Everything is quiet and peacefully. Maybe this damned Swordfish had had a false signal and there hadn’t been any submarine at all. If not, the waters around him will soon swarm with German submarines. Soon he will leave the area of the Gibraltar air patrols, and then he can only rely on himself.
Walker thinks about the course to Liverpool. The usual one would be westwards, until the middle of grid square CF, and then straight north to sail west of Ireland. The usual one. The convoy would be quite far away from the occupied coast of France, where the Germans have their bases. The course is still within the range of the German planes, but they would not have much time to cruise there. There are two drawbacks, though. First, the course is longer and therefore the submarines would have more chances to attack. Second, the course is well known to the Germans as well.
Walker is wondering about another course, closer to the Spanish coast, closer to the bases of the Germans. If the convoy would sail right between CF and CG, the journey would be significantly shorter. However, a risky plan!
And there is still a third option. He could stay on course southwest for a while. If his German attender sends this course to the other German boats, they may wait for the convoy further south. Then, when Walker changes to course to north, they may be far away and maybe loose the contact. And there is still the other convoy behind them, which destination is Freetown.

Which is the right course:

A) Take the usual one. It is a good compromise of distance to the German bases and length of the journey.
B) Take the short way home. It is closer to the German bases, but we will be sooner at home and the submarines may have less chances to attack.
C) Stay on the southwestern course for a while. Maybe this misleads the Germans.

P.S.: Welcome Napoleon!

[Fisherking]

C Stick it out for another day before turning West Northwest for a while, then take the Northern course.

[King Kurt]

Definately C and change course as night falls - quite early as it is December

[ELITEofWARMANGINGERYBREADMEN88]

C,I Agree.

[Kagemusha]

C it is.

[Franconicus]

Chapter 6 – night of 15./16. December

The ships are still constantly running southwest along the coast of Morocco. This is the normal route to Freetown and every mile brings them further away from their destination Liverpool. Hopefully this is suitable to mislead the Germans, because it certainly makes the journey longer and gives the Germans more time for attacks.
The convoy now sails in grid square DJ18.This means that it left the air cover provided by the Gibraltar squad and is now left on his own. All day long the planes of the Audacity encircle the convoy. The only connection home left is the radio. Western approaches command shows that it still cares for the lonely convoy and send three messages:
1) There is another convoy about 40 nautical miles behind. It is bound for Freetown.
2) There are about six submarines close to the convoy.
3) There is a storm in the Atlantic, but the convoy should have at least another day with rather good weather.
Night falls, Walker alerts the crews of the escort ships. He knows that the Germans are out there, even if he cannot see them. However, nothing happens. At midnight, the convoy is right in the middle of grid square DJ18. If it goes on for another day, it will pass the Canaries. Sooner or later Walker will have to change the course to west or northwest. The three escort destroyers Blanckney, Stanley and Exmoor are the fastest ships of the escort and very useful for hunting submarines. However, these three ships have only a very limited range and will have to return to Gibraltar on December 18 or 19. Maybe just when the German submarines are starting to attack. Walker still wonders about the right course when the radio operator receives a distress call. It comes from the “Empire Barracuda”, which is obviously attacked by a submarine. Looking at the coordinates, Walker sees that it must be a ship from the Freetown bound convoy. Poor boys!
It looks as if the peaceful period of the journey is over. This may be the signal for opening the battle!

Tasks:
1) Decide about the course.
2) Any measure against the submarines?

[Fisherking]

The convoy should zigzag at five minute intervals. Sub commanders have to observe, target, and fire. It takes time to do the trig once the course is plotted and run times for torpedoes is typically about 2 minutes. Frequent changes of 45°-60° would make targeting of the ships difficult. If submarine contact is made then the convoy should make a 90° turn away from the contact as directed by the escort commander and make course changes every two minutes while contact is ongoing.



An example:
/
\
/
|
\
/
\


We should make a turn to the west at once and continue for about 12 hours. then turn North West for 24 hours before settling on our homeward course.

[Franconicus]

I am not an expert on this, but it seems hard to change the course of a big ship every two minutes. Even harder to change the course of more than 30!

[Fisherking]

The ship may take a little time for the ship to respond and to settle on course but it is a matter of changing the wheel the number of degrees to bring about the settings.

If you think it is too frequent we can double the times but it dose diminish the effect.

[King Kurt]

I think 2 minutes is too quick, especialy with an ungainly convoy. I think every 20 -30 minures is more in keeping.

[Fisherking]

The idea is to make it difficult to target the ships. 5 to 10 minutes may do that but 20 to 30 minutes is a very minor inconvenience at best.

In that amount of time a Skipper could set up complex shots, targeting 5 ships, launch all his torpedoes, and be almost reloaded before we changed course to foul any shots.

While 2 minutes is difficult, it is only while the convoy is under attack. If you think it is too frequent leave it at 5 minutes and 10 when not under attack.

It is stressful on the helmsmen but not so stressful as being sunk. We want the convoy to have a plan of action so that the ships don’t panic. It is as much a morale factor for us as it is a deterrent to the Germans.

It also means that the subs have to close to a much closer range to get a good shot which also means we have a better chance to detect and kill them.

To get a good shot the U-boat might even want to surface and risk a couple of quick launches before diving and running away. That puts him in our sights and even the gun crews on the merchant ships might get in some shots.

The frequent changes keep helmsmen alert and under attack it keeps there minds off worrying about being hit. Otherwise they will be watching the water for wakes or imagined wakes and zigzagging on their own, which dose not keep the convoy together.

[King Kurt]

Fischer

While your comments would be true for individual ships, we must remember that the convoy is made up of lines of the order of at least 5 ships long. Each line would be about a 1km long. The turn would be about a single piont, so the rear ships would have to travel to the turn point before turning. At 12 kts that would take at least 3 to 4 minutes. Moreover the ships do not turn on a sixpence, so the act of turning would take some time. Also, at night, such rapid maneavers would lead to collisions.
I found this on another forum
"The Zig-Zag patterns used by Allied convoys were VERY strict and difficult navigational evolutions... in fact, the Navy sailors used to joke about worrying MORE about getting run over by a freighter than hit by a torpedo.

Each Ships Captain would receive a plan with a series of "Zig-Zag Plans"... so once underway, the Convoy Commodore could order by flashing light a specific "plan" based on a base-course. For example: "Zig-Zag Plan 10, 110* " would mean a base course of 110 degrees, with a 15 degree turn to port after 20 minutes, a 20 degree turn to starboard after 30 minutes, a 25 degree turn to port 15 minutes later, and then a 10 degree turn to starboard after 25 minutes... REPEAT"

One of the KEY problems with the Convoys, is that they moved at little more than 10 knots (11.5 mph), and more often at 6 knots !! A German submarine could move on the surface at almost 18 kts (20 mph)... twice as fast as the convoy.

SO, the Zigzag was used to confuse the fire-solution of the U-Boat... a steady course is EASY to determine when to shoot, it's like leading with a shotgun. IF the target(s) are making random (but coordinated) course changes it either throws the solution out the window, OR forces the sub to approach closer. THIS makes the sub more susceptible to detection and counter-attack.

The freighters move in a "tight" group, zigzagging, while the ASW escorts (Corvettes, Destroyers and Frigates) roam about like boarder collies. The submarine plots it's fire-solution by basic navigation skills, and since this in the days prior to computers, a well-timed "ZAG" can negate the weapons officer's computations.

Zig-Zag navigation went out the window pretty quickly in World War II as a result of:

Faster cargo ships
More escort ships
Better equipped escort ships with ASDIC (sonar) and Radar
Escort Carriers (subs HATE airplanes !!)
British cracking the German codes - NOW you just AVOID the subs."

So it may be possible that our convoy might not even ZigZag at all. However, assuming it does, the abovesuggests that the periods are 10 to 25 minutes and random. also, I believe we would be unlikely to zigzag during the night - there was too much of a risk of collisions.

[Franconicus]

Deadline on Sunday, that's alright?

[King Kurt]

Deadline on Sunday, that's alright?

OK with me. I am with Fischer re the the course - the subs are north of us so we need to go west first, before heading NW. The 3 escorts who will have to leave we will put between the convoy and the subs - i.e. to our rear/ right hand side of the convoy. Finally we should head for the storm - bad weather is our friend.

[Fisherking]

I think we are in agreement for the most part.

We can use a longer zigzag.

However, I was not thinking of columns making turns but individual ships maintains approximate stations but turning. If only the leading ships turn it defeats the purpose of the zigzag. Then it is only a course change. They are still ducks in a row to be hit by aimed torpedoes. If each ship turns at a precise time on a precise course it is another matter.

The convoy is arranged in a box formation so that it reduces chances for collusion, keeps structure and cohesion, and need not reshuffle position. The Convoy Commodore is not the leading ship but nearer to the center of the convoy to maintain control. The other ships should more or less wheel about him.

If you think of the formation as marching men the zigzags are not column movements but flanking movements, or half flank in this case.

If you don’t think they have enough time to practice this or that professional merchantmen are not smart enough to navigate a water ballet, we can just drop it.

[Franconicus]

Just one question to get you right: zigzag at daytime, night or all day long?

[Fisherking]

So it may be possible that our convoy might not even ZigZag at all. However, assuming it does, the abovesuggests that the periods are 10 to 25 minutes and random. also, I believe we would be unlikely to zigzag during the night - there was too much of a risk of collisions.

I guess we will go with daylight hours. But if attacked at night we had better make some sort of change.

[King Kurt]

Just to let you know, I am off on my hols from today, so will be offline until 26 april - don't sink too many subs while I am away!!

[Franconicus]

Chapter 7 – 17. December

December 17th, at 0:00 Walker gives the convoy the signal to turn west. In the darkness the ships turn away from the African coast to the wide Atlantic. Walker hopes that this maneuver will lead them away from the submarines.

At 1:30 STANLEY and SAMPHIRE report that three ships are missing, the Blairatholl, Thyra and Ocean Coast. Lt Cdr FT Renny, captain of the SAMPHIRE, asks for the permission to search for the lost ships. Walker swears like a trooper. This is a fine moment to loose contact, now that the Germans are so close. Walker hesitates. Sending escorts would weaken the protection of the rest. He could fire some flares, but that would show their position to the enemy, too. Walker still wonders what to do when he gets a new message from the SAMPHIRE that the three missing ships are returning.
At daybreak the Martlets get off for their daily duty and the convoy begins to zigzag. This slows down the cruising speed to 5 knots, however. At noon, the convoy just passes from grid square DH 3944 to 3866, Walker makes it turn northwest. The journey is still peaceful, the air patrols have nothing to report. The sky is cloudy and a fresh wind is blowing the clouds westwards.
One hour later, Walker receives bad news from the Audacity: one of the Martlets has an engine failure and it difficult to repair it on board of the carrier. Therefore, there are only three combat-ready planes left, not enough for a permanent patrol. Furthermore Mac Kendrick tells him that he is going to stop the patrols as the wind is getting too strong.
Radio messages from England report, that there are still several submarines close to the convoy and that a storm front will come in the next 24 hours.

1) Course?
2) Other orders?
Have a nice holiday! And KK: Beware of subs!

[King Kurt]

I have returned refreshed from my family holiday!! Despite 2 sea journeys on the Isle of Wight car ferry, we managed to avoid any wolf packs lurking in the Solent - no doubt to my superior tactics!!

so - to work. the storm will be our friend - worse news for the U boats rather than us. I suggest the following:

1) Zig zaging is slowing us down - we should cut back our course changes to say twice an hour.
2) We should steer best course for home, taking into account the lesser Zig Zag
3) We should maintain our inner and outer ring of escorts.
4) We should ground all aircraft - which sounds like it has happened already. However we should urge one patrol a day - say at dawn - if at all possible with the weather. When the weather improves, we can go back to as best air coverage as we can.
5) During the night, we should arrange a fake attack with snowflakes etc to the east of the convoy. Our destroyers who have to return to Gib are there, so it would be good to try and make use of them. All merchants will be informed of the fake attack and it must be stressed that they should not fire their snowflakes.

Any thoughts fellow sailors??

[Fisherking]

I too have been away due to technical problems.

Anyway, it all sounds good.

Do it.

[Franconicus]

Chapter 8 – Noon, 18. December

Walker continues his march through the Atlantic Ocean. The leader of the Liverpool bound convoy decides that the time for detours is over. He conveys the captains of the other ships to reduce the zigzags to two turns per hour. He also announces that the convoy will turn northwards during night to take the straight way home.
The weather is getting worse and huge seas reduce the speed of the convoy to some 6 knots, however. There is nothing Walker can do to raise the speed, but at least the Krauts will suffer the same way.
The air patrols have already been stopped and the convoy has to rely on the lookouts. But during daytime of the 17th, nothing happens. After midnight, Walker gives the signal for the three destroyers and soon Blanckney, Stanley and Exmoor sheer out of course and disappear in the night. Soon Walker can hear the sound of detonating ash cans and the shine of snowflakes. The three destroyers are doing a good job to pretend a combat and Walker hopes that his trick will work and lure the Germans away from the convoy. He waits a couple of minutes and the he gives the order to turn northwards, away from the three destroyers and hopefully also away from the enemy.
At 2:00, however, he receives a message that one of the merchants claims that he has spotted a periscope. It is the Benwood, a freight ship in the middle of the fourth column. Minutes of anxious waiting follow, but nothing happens. The merchant ships keep their nerves and stick to the orders.
At 2:42, Lt. Cdr. Sayers from the HMS Rhododendron reports a short ASDIC contact in the western forefront of the convoy. However, the contact soon disappeared.
Walker has to face the fact that the Krauts are still out there waiting for their chance to prey and that the escort is significantly weakened by the withdrawal of the destroyers and the loss of the air patrols.
Fortunately, day breaks and still all of the ships are alright. Walker receives a message from the Audacity. Mac Kendrick complains that the Audacity has lost her escort and is now without any protection.
At December 18th, 12:00, Walker marks the position on his map. It is the cross between the squares CF99, CG77, DH31 and DH32. The convoy is still marching northwards with a speed of about 6 knots. The storm is getting worse and Walker hopes that he can keeps at least the 6 knots.
1) How to rearrange the escorts now that the destroyers are gone?
2) During night, the convoy will pass a awful storm. Any orders regarding this?

[King Kurt]

I would suggest the following for rearranging the escorts.

1) replace the 2 destroyers from the front group with 2 corvettes - so forward group is Stork + 2 Corvettes.
2) Put a corvette on each corner of the convoy. They will patrol the flanks and rear of the convoy.
3) Put Audacity between the front of the convoy and the front group of Stork + 2 Corvettes.
4) This leaves 1 corvette which will take station at the rear of the convoy in the middle. It will lie slightly off the rear of the convoy so it can move to assist on either flank if the convoy is attacked.

As for the storm, we need to use it as much as possible without putting the ships at risk. Franc - could you give us some information on the storm and where it is in relation to the convoy and the UK. For example if the storm is coming in from the West, could we skirt round the storm leaving it to the east of us - i.e. between the convoy and the French/ Spanish coast?

[Fisherking]

I disagree strongly.

The strongest reaction force belongs at the rear and so does the carrier.

Let me get the number of escorts straight.

We had 9 and were reinforced with the 3 of the carrier group?

Now we lost those three and still have the 9 and the carrier?


I would recommend that we have two corvettes at the front and on the flanks.

The two destroyers and a corvette at the rear.

One of the destroyers can reinforce a group where it is needed when a sub is found, but two always need to protect the rear of the convoy.

If the escort is too weak it will invite a surface attack by the U-boats, which is far likelier to succeed than a long range submerged attack. Also at the rear the carrier is afforded better protection. She is every bit as vulnerable as a merchant ship while sailing unescorted.

If we are getting contact reports we need to steer west for a few hours to try and lose them until the storm hits.

Then it is likely we need not worry too much until it blows its self out.

Subs at periscope depth are also effected by the storm and waves. They can even be thrown to the surface.

Report the several contacts and request some reinforcements. It will take days for them to arrive but it is better to alert them now than have to wait while we are in contact and losing ships.

[Franconicus]

Your escort force currently consists of:

2 sloops Depthford and Stork
7 corvettes : Rhododendron, Marigold, Convolvulvus, Penstemon, Gardenia, Samphire and Vetch
1 escort carrier Audacity (Cdr MacKendrick)

In total 10 vessels.

A big storm front is coming from west to east; it already hit you, but the centre is still coming!

[King Kurt]

The position of the escorts depends on where you percieve the threat is most likely to come from. I would have thought that is most likely to come from the front of the convoy, not the rear. U Boats are not fast boats, even on the surface, so they would want to position themselves in our path and attack accordingly. They would have to travel significantly faster than us to come up behind us. I placed the carrier between the front screen and the front of the convoy as that position, on my deployment of escorts, would be in the maximum level of escort. I had also missed the sloop Depthford from my calculations, so that could sail as close escort to the carrier.

Also we are trying to have a 2 layer approach so the U boats have to fight through two layers. The front group are several miles in front of the convoy so they can attack any subs detected. fischer - why do you think our threat is most likely to come from the rear?

As for the storm, I would be hesitant to turn to the west - our most recent detected threat was to the west and by turning to face the storm we will be slowed even more. My inclination is to press on to the North and only turn into the storm - ie to the west if the storm gets so fierce that we need to face it head on for seakeeping reasons - ie to stop waves hitting us side on.

[Fisherking]

U-boats are faster than our corvettes.

They us their surface speed to position themselves for an optimum position for attack.

Directly a head is not that good of a position. It is better to be slightly to the flanks. Head on shots are very likely to miss.

However stalking and trailing the convoy is from the rear. That is where you will most likely see them surfaced. The rear flanks are also where it is easiest to get inside the convoy with a dash on the surface at night.

The Destroyers are considerably faster than the corvettes and the U-boats. Having them in the rear is the best place to reinforce on of the three groups, should they make contact with a U-boat.

Should the front group contact a sub we want to change direction for a time to avoid it anyway.

When and if we are reinforced by more escorts we will strengthen the front group first of all. But at the moment we have early enough to cover the convoy and the escort carrier is a big target. The rear is also the best location for command and control.

We can maintain this heading for a time and then try to shake them off in the storm but if the convoy is sighted the pack will spread out to form a cordon. Until we have clear weather and air cover things are going to stay a bit dicey.