I have been finding (GWX3) steadily small convoys with large troop transports on them along the east coast. The real U-Boots found mostly small units, but unfortunately SH3/GWX/NYGM etc. lack 1000 ton ships, they are mostly 2000+ tons vessels. In GWX you can find some, but a more accurate representation of the Black Sea theatre of operations would have meant smaller vessels. Overall, it is anyway a great campaign in GWX3, I loved the detail in populating harbours, giving nets and minefields where appropiate, etc.
A campaign sure worth it.