 Complete the following phrase:  In the Mediterranean the submarine force suffered heavily in the face of intense anti submarine warfare, and in attacks on heavily guarded convoys and naval formations. Results were modest, with only 21 merchantmen and 13 enemy warships sunk for a total around 100,000 tons; one reason for such a disappointing score was the lack of targets with most of them being harder-to-hit warships, and the merchant ships being under heavy escort, and another was the outdated doctrine employed at the beginning of the war with static patrols, and attacks being executed firing only one or two torpedoes, although this aspect was being corrected by 1942 as proven during 