Post by aeson on Jul 13, 2019 14:54:20 GMT -5
Let's look at a map:
Say that I'm Russia trying to escort convoys through a French blockade, and that my ships can stay at sea for 5,000nmi regardless of how fast they're steaming (unlikely in the extreme, but whatever). Say that I need to escort convoys from the Skagerrak to the Orney-Shetland area to get them through a French blockade - roughly 300nmi. How many times can I do this in a single sortie? Well, I need to use ~1,100nmi of my ship's cruising range to get out of the Baltic and then back to port (possibly closer to 1,300 if I'm sailing out of, say, Riga), so that leaves me with 3,900, which is 13 300nmi trips; I have to give up one of those because my ships don't have the range to make the return trip. Assuming a convoy speed of 10 knots - which is fairly fast by WWI standards and still isn't too shabby by WWII standards - it'll take my ships about one day to escort a convoy across the North Sea, which means that I can escort three convoys in and three convoys out in a week, and then I need to return to port. That's if nothing happens that forces my ships back to port sooner. Due to the time taken to get from the Skagerrak to my nearest ports, I can only do this about every other week, at best, so if I have to escort convoys with a large part of my battle fleet then I can only escort about six convoys in and six convoys out per month. Next note that for a French blockade force based out of Brest, intercepting Russian merchant shipping between Britain and Iceland isn't actually all that much worse than intercepting Russian merchant shipping while it's in the North Sea - it's a ~750nmi transit to blockade stations in the North Sea or an ~850nmi transit to blockade stations between Scotland and Iceland, but it'd roughly double the distance that I'd have to provide escort to get convoys through the blockade, thereby halving the number of convoys that my fleet can escort while at sea.
This, mind you, is a very optimistic assessment of the number of convoys I can escort through the blockade zone with the bulk of my battle fleet - I will almost certainly have other things I need to do with my ships, and at some point the ships will need to be maintained and the crews will need to be rested even if nothing noteworthy ever happens at sea. I'm also ceasing to protect my convoys long before they could arrive anywhere but Britain, Germany, the Low Countries, or Scandinavia, and trade with Germany and a large part of Scandinavia wasn't going to be interdicted to any significant extent by a blockading force in the North Sea anyways. On top of that, typical convoys probably aren't averaging ten knots until at least the second quarter of the Twentieth Century even if you don't have problems with poor station-keeping or straggling merchants slowing the convoy down.