Complex sentence: In the mid 1830s, "Terror" was refitted as an polar exploration vessel; her previous service as a bomb ship meant she had a strong framework to resist the recoil of its mortars that could similarly withstand icebergs and pack ice.
Split into simpler sentences: In the mid 1830s, "Terror" was refitted as an polar exploration vessel. Her previous service as a bomb ship meant she had a strong framework to resist the recoil of its mortars, that could similarly withstand icebergs and pack ice.