Yep, you should be able to knock out both their big fleets (plus the Canadian ships) G1 setting them back for quite awhile. With a couple subs here and there and the Luftwaffe you can keep them from building ships around England for a couple turns and they are forced to build a starter fleet off Canada. Even building off Canada isn’t to easy early on if the wolf pack is in tact because of the 1:1 detection ratio, and there is no airbase to scramble in Canada when they see your subs. It forces them to spend $ on ships, and less on resources elsewhere.