Snorkelling

[RoaldLarsen]

Originally Posted by Lt.Fillipidis

Yeah but you can hear a ship while submerged way before it can detect your snorkel. And in a bit more rough seas, detecting your snorkel touches the limit of impossibility.

I don't worry much about surface ships. Only one of my 19 losses has been to a lone warship or a hunter-killer group. Nearly all my losses since late 1942 have been to aircraft. So I am concerned with how detectable the sub is to aircraft.

I agree that the snorkel gets detected too easily in rough seas.

Originally Posted by Randomizer

Most of my SH3 patrols are late war and so have spent a lot of time snorkelling although I carry few of the objections thrown out here. I spent a fair bit of effort learning how the U-Boats operated inshore in the late war period and applied those techniques to SH3.

I agree with almost everything Randomizer has written here except:

Originally Posted by Randomizer

4. Once you decide it is no longer safe to transit on the surface, cruise submerged at 3 knots and snort two or three times a day or when the battery is down to 85% or so.

I use 1.8 knots. 3 knots is more realistic, but 1.8 knots is safer.

Originally Posted by Randomizer

7. Contrary to what is often written I do not agree that you are as detectable snorkelling as you are on the surface.

How much data does Randomizer have to go on? I have run about 40 patrols in snorkel-equipped subs. I'd have to say that detections per unit of time snorkeling is between 75% - 90% of encounters per unit of time surfaced. ("Encounter": my crew sees aircraft; "detection": aircraft attacks me) Given that about 10% of surfaced encounters do not involve the aircraft actually detecting the sub, that means the detections of snorkeling subs occur about 85% - 100% as frequenty as detections of surfaced subs. Tarnmatte can reduce the detections by about 10%, but it wasn't commonly available on operational u-boats.

Against the insignificant improvement in detectability of snorkling over surfaced recharging, one must weigh the the fact that a snorkling u-boat, even with observation scope up, is much less likely to detect attacking aircraft in time to evade attack than is a u-boat surfaced in daylight. This means that a snorkling u-boat detected by aircraft is much more likely to be damaged by those aircraft than is a surfaced u-boat.

If Randomizer has a similar quantity of observations, but different conclusions, could it be because of different areas of operation leading to different aircraft being involved? Not as many of my missions were inshore. Inshore missions seem to run into small aircraft more often and these seem less likely to be equipped with RADAR. I've noticed that single-engined aircraft, though smaller, are more likely to be detected by my crew without the aircraft detecting my sub than is the case for multiple-engined aircraft.

My original comment about detectability specifically mentioned centimetric radar, and most of the attacks on my snorkling u-boats has been by aircraft equipped with centimetric radar. Perhaps detection rates by Hurricanes etc. are signifcantly lower, but I wouldn't have noticed that.

Anecdotally, my most recent trip to the North Channel in 1944 resulted in the loss of my most successful 11th Flotilla commander (7 patrols from 42/10 to 44/05, 163kT sunk). He was attacked by aircraft... while snorkeling.