 During the month of April 1917 , German U @-@ boats succeeded in sinking 860 @,@ 334 tons of Allied and neutral shipping , a total unsurpassed by any month in either of the two world wars . U @-@ 70 's contribution came in the form of ten ships of 23 @,@ 530 tons sent to the bottom , four of them on the same day , 24 April . 
