[CCIP]

There were plenty of convoys and on the approaches to England they were generally escorted, including by large surface units to protect against German raiders - the convoys were only left unescorted further out in the ocean.

I think you're interpreting the lack of historical attacks on convoys as a lack of convoys as such, and the British concern over their ability to escort them as a lack of escort. Neither is true. In fact the lack of attacks on convoys has more to do with the fact that the Germans had very few boats available at the start of the war, these numbers being too few to execute Doenitz's successful wolfpack tactics. It's not an easy task finding a convoy with just one or two boats, and an impossible task sticking in contact with it (something that SH games don't make obvious enough). Even a small (but competent) escort can deal with one boat - something Doenitz realized from the start. Make it a half-dozen boats, and then even a heavy escort might struggle - but you need to actually have those boats available and deployed to hunt that convoy first, something that's hard to do with what was at best 30 ocean-going boats in total in the first year of the war. As a result, only a few convoys were subject to attack - which, more than anything, is an indicator that the convoy system was in fact quite successful from the start. However U-boats had plenty of other targets to hunt at that time, and so they were simply not deployed to actually hunt down convoys until enough boats to actually became available. It wasn't until 1941, though, that wolfpack tactics and with them substantial convoy battles really started happening in earnest. But again, that's really not an indication that convoys weren't there or were unescorted - this had much less to do with the British situation and more with the Germans' initial lack of boats.