The Invisible Enemy

[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??