Complex sentence: The ferries of EFO had good armament, but they were far too slow and too small range for operations and made them almost sitting ducks to the Soviet patrol boats, gunboats and bombers.
Split into simpler sentences: The ferries of EFO had good armament, but they were far too slow and had too short a range for effective operations. They were almost "sitting ducks" to the Soviet patrol boats, gunboats and bombers.