no 'she's going down' text = no sink credit?

[OuNiS]

Ok. It was dark, stormy night (Wind 15 meters/second).
I discoverd 5 maruders from convoy (large convoy).
These ships couldn't travel with speed 7 kts (as a convoy) and they sail at the back of convoy. They looked very poor. Speed about 3 kts. I fired 3 torpedoes one for each ship. All of ships was hit but text shes going down didnt show and I had no credit for these sinkings. Who could tell me why?