desert stronghold

[storerov]

i´ve completed all the objectives, but i can´t get into the stronghold.

there are some secondary objectives left; 'sink the battle ship' and 'sink the transport'

i´ve sunk three transports, but they keep comming, do i have to sink a curtain amount or?

i´ve sunk a ship with howitsers on, and can´t see any other, where is it?

main subject, how do i get the game to progress?