Let's say a U-boat on an average day can spot and intercept a freighter at 30 miles, (smoke over the horizon). If the ship is advancing at 10kt then over the 12 hours (or whatever) of daylight, the ship is vulnerable in slice of sea 60 miles wide and 120 miles long - 7,200 square miles. So, let's say 10 ships are sailing independently. Their total area of vulnerability in 12 hours of daylight is about 7,200 x 10 = 72,000 square miles.SpicyJuan wrote: ↑21 Oct 2019 06:19Regarding convoy tactics (I don't know too much about this subject), weren't they made possible/effective by the U.S. joining the war and greatly contributing/freeing the RN to supply convoys with escorts? Assuming the U.S. doesn't join in, are the convoys even possible without additional escorts and ship production?
Now, let's say they're sailing in convoy maybe 500 yards wide and 2000 yards long, (or whatever). Let's say the additional smoke and larger formation allows the U-boat to spot them 15 miles further away. So, there will be for 10 ships a slice of vulnerability of 90 miles x 120 = 10,800 square miles. Versus 72,000 square miles. The ten ships collectively therefore have a far smaller 'footprint' at sea and are much more likely to slip by. This is true whether they have an escort or not.
So, if a U-boat sees them and attacks, then the question is, can the U-boat sink more than one ship in it attack? That's where the lack of escort get dicey. If the U-boat can sink, say, 5 of the ships, then the advantage of convoy isn't so much. But, if it can only sink, say 1 or 2 ships, then even without an escort, the convoy is a big advantage. The answer (IMO) is that if the convoy has no escort, but the ships themselves have deck guns for defense, the submarine might only get 1 or 2 kills before the convoy is gone. So, still a net advantage.
This is where combined arms warfare at sea plays a role and the lack of support of U-boats by the German surface navy was important. Because, whereas a U-boat is likely not to sink more than 1 or 2 ships in a convoy, in the few surface attacks made by the HSF on convoys in 1917, even a couple cruisers could pretty much eliminate a convoy even with 2 destroyers escorting. So, convoys were great for protecting ships against submarines. But, for superior surface forces, they could be a death trap that made the warships' job easier. Hence, the German failure was in part the introduction of convoy tactics and in part the failure to counter with wolfpack tactics. But also, the lack of activity of the surface fleet to assist the U-boats n 1917-1918, even if at great cost to the surface fleet.