Prior 1944, the P-38 (or any US aircraft) will do much more harm to Axis ships if it uses bombs - they are far more reliable, readily available, and a hit by a 500, 1000, let alone 1600 lb AP bomb will put many a ship out of commission. The aircraft carrying a torpedo is a far easier target than a bomb-carrying one. It is easier to hit a small target, say a destroyer, by a bomb in a low-flying aircraft than with a torpedo.
In 1943, the mast-height bombing and skip bombing were perfected enough to be viable, dive bombing more earlier.
The Val dive bombers sunk heavy cruiser HMS Dorsetshire with 250 and 500 (actually 551 lbs - 250 kg) lbs bombs; looks like it was 10 bombs total? One of the bombs detonated the ammo magazine, those tend to be well armored. HMS Cornwall was sunk by same bombs, 8 hits.
The SBD-1 (= the 1st Dauntless version) carried not just 500 lbs bomb, but also 1000 lb GP bomb and 1600 lb AP bomb. So Id say that the Dauntless with a 1000 lb, let alone 1600 lb bomb was in a good position to harm any ship they can hit.