GWX - Early War merchants more difficult to sink?

[IRONxMortlock]

I'm currently on my 2nd GWX career (as per my sig). I found ships much easier to sink in 1942 than in 1939/early 1940. For large merchant ships two torpedoes was almost always enough in 42 and small ships would generally go down with one. However now (39) I find I commonly need more than two for large merchants and at least two for small ones.

For example, in my last patrol in 39 I came across a convoy. In my first attack I fired 1 fish at a pyro and 2 at a large merchant. The pyro exploded immediately but the large merchant had water washing over it's decks but wouldn't go down. I raced ahead and hit the same convoy again two hours later. Same tactic; 1 at another pyro and 2 at another large merchant. This time the pyro didn't explode and the large merchant just kept on steaming. Now I was out of fish so I turned for home with only one 6000GRT pyro sunk.

Has anyone else noticed a difference? Perhaps it's just more noticeable to me now because with a Type IIA I only get 6 fish as opposed to the 21 I had with my IXC?
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