Zosimus opined:
Indeed - the "safe arming" distance. It was possible for a torpedo to malfunction and "return home", or even for the fuse to detonate prematurely. Premature detonation happens sometimes in SH3, particularly for magnetic settings in rough weather, though generally at a safe distance from the tube. The practice at the time was to fit an arming device - a threaded screw attached to a locking pin. A small propeller on the nose was geared to wind the screw to slowly withdraw the locking pin and so arm the fuse.
http://www.uboataces.com/weapon-torpedo.shtml

However, bear in mind that the 300 metres is the distance the torpedo has to travel before the fuse is armed, not the range to target when it's fired. A torpedo fired at rather less than 300m at a fast retreating target might arm itself in time, whereas one fired at say 350 metres at a DD rushing straight towards your boat at speed may well not.

AK3389. Convoy sighted. Outbound. 9 knots. Course... 230ish? I am directly in the convoy's path.

Cannot reload external torpedoes. Gale force winds. Heading 220 speed... 8 knots or so. One eel in the back. Hoping for the weather to change.

April 4, 1943. Leaving Lorient for DO98. Patrol expected to take at least a month. We are equipped with the finest anti-air weapons available, skilled anti-aircraft officers, and a watch officer who is skilled in anti-air tactics.

I have also managed to get T3 pattern running torpedoes. I have two. I don't know how well they work, so this will be my chance to try them out.

May 1943 is right around the corner.

Patrol aborted early. One was plane shot down. However, four men were killed. After two hours on the bottom in 110-meter water, we stopped the leaks, blew ballast, and returned to Lorient. Total patrol time... about 5 hours.

U-66 is kaput.
I am now commanding U-851 a new IXD2.

One of my two current careers was started at the latest possible date in 1943, so I could get command of an IXC with a (relatively) experienced crew. On the last patrol out of Brest, we were attacked by so many large aircraft, in very unrealistic numbers, before reaching deep water on the way to the Caribbean, that I almost aborted the mission and gave up totally. Especially watching Sunderland FBs dive-bombing us, some climbing vertically after dropping bombs or DCs. A vertical Sunderland is an ex-Sunderland, whichever way the nose is pointing when it's flying vertically. The fuel and bomb loaded weight of a Sunderland was around 29 tonnes. I guess there's just one "flying model" in SH3, simply modified for aircraft speed.

After my gunners had accounted for a total of 50 large aircraft, in the first 250-odd km, probably more than Coastal Command had at any one time in the entire SW Approaches, I aborted and restarted from my standard "Outbound" save, where I've plotted the route to the target grid, avoiding aircraft hotspots like the Azores, and passing across likely convoy routes. Result - no aircraft attacks at all, though a few Sunderlands and Wellingtons were spotted some distance off, turning and flying away.

Wellington crews seem to be as blind as my sonar man is deaf and dumb - one even flew right over us in the early dusk - no reaction at all, despite it sprouting radar aerials like a hedgehog.

August 1940, U-22 (IX-B)

Departed Willemshaven on Early june, with a refuel in Spain. Tried going for Cape Town (South Africa) but due a fuel leak, BDU has ordered us to patrol around Lagos (*The port east of Takoradi, forgot its name, already closed SH3)

We saw a large merchant anchored about a kilometer out of the harbor, promptly sunk it.
Used 2x TII

BDU ordered us to Freetown next. Sighted a small merchant, about 50km west of Freetown. shot off one T1, hit about 1/3 from the bow causing the bow to lay deeper in the water. She remained afloat however. Due to bad weather, couldnt use the deck gun, but wasn't worth a torpedo. We gave chase for 7 hours before the weather calmed down enough for the deckgun. 9 shots below the waterline sunk her. The cargo remained afloat, used our AA to sink it.
Used; 1x T1, 9x 105mm, about 30 30mm and 80 20mm.

Remained submerged for about 5 hours, listening for any ships coming to aid, nothing. Headed towards Freetown on surface with 7 knots.

Kplt Malifozik, U-122

If an aircraft doesn't carry any bombs, it simply won't attack you. But if it is a fighter, it will dive and open fire on you with its mg guns ! Epic moments !!

U-65
 

October 1939 , AM 52
Wind 15 m/sec , sea state : harsh
Traced and intercepted British small merchant
Fired 6 TIs against her
2 premature explosions spotted
2 explosions on target seen
2 unaccounted for.
Target sunk.

A total waste of expensive torpedoes for such a small target.

Update
Just fired my last 2 TIs at a medium merchant (6000 grt) under the same weather conditions. Both premature explosions. No internal torpedoes left. She will move on.

U-105 1st Patrol (Pt. 1)
 

That puts us in the same flotilla, roughly at the same time (I'm at JAN 1st 1941, just left on another patrol on DEC23

Good luck :Kaleun_Salute: I hope you have more luck with your eels than I've been having with mine!

((Que https://www.youtube.com/watch?v=VLguQtArm8A ))
No luck with torpedos. 3 duds, 1 ran deep and 1 hit for 4000grt merchant. finished her with deck gun action

Uneasy times, eh? I'm hoping my next encounter with a merchant goes more to plan than the last two! Not had much luck with this lousy weather, either...

KingOfNothing22 wrote:
Type I fish fired at fast speed will often detonate prematurely if using magnetic setting. At 1500m I'd use medium speed with magnetic.

Thanks for the heads up Rambler I'll be sure to keep that in mind!

I didn't write down what speed I fired them at but if I remember correctly all but two of the torpedoes fired at the convoy were fired at medium speed (four of which detonated prematurely, with the other two missing) and the others were at slow speed, 1 of which also detonated very quickly after firing.

I don't tend to set them to fast as I like to attempt to get some distance between myself and a target in case of escorts (in the case of convoys), so I can't say whether I've had any premature detonations using them at fast speed.