In the Northern front I start to retreat 1 hex row so the infantry corps cant get a full round of attacks. The arm corps have left so now only inf in the north.

ORIGINAL: malkarma
The BoA can have a snowball effect if the UK loses too many escorts, but not because why some players could thing.
The critical issue with the escorts loses is not the cost to replace them, its the time. New escorts need 200 days to be built, so what happened to you will need around 250 days to replace those loses unles you put several escorts per turn in production. So during that time not only your convoys will be more vulnerable, but also the german subs will suffer less damage.
If in the combat calculator there is no aspect of the equation where escorts reduce the chance of sinking an MM then this is contrary to the manual (p.22 & p.83).ORIGINAL: Harrybanana
If by "your convoys will be more vulnerable" you mean that an unescorted convoy will suffer more losses than an escorted convoy than I don't think that is true. Unless a change has been made that I am unaware of, escorts have no effect on how many MS are sunk.