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## HMS Terror and HMS Erebus: The Ships Before the Expedition
The two ships that carried the Franklin expedition were not built for Arctic exploration. They were bomb vessels — ships designed to carry heavy mortars for bombardment of coastal fortifications — which had been converted for polar service by reinforcing their hulls against ice pressure and equipping them with auxiliary steam engines.
HMS Erebus had been built in 1826 and had a distinguished service record before the Franklin expedition. She had sailed with James Clark Ross’s Antarctic expedition of 1839–1843, navigating into what is now known as the Ross Sea and reaching further south than any expedition had previously gone. The Antarctic voyage, under the command of James Clark Ross with Crozier as captain of Terror, had demonstrated that bomb-vessel conversions were well-suited to polar conditions: the heavy construction that made them effective platforms for mortars also gave them the structural strength to resist ice pressure.
HMS Terror had been built in 1813 and had an even longer service history. She had participated in the War of 1812 — she was the ship that bombarded Fort McHenry in Baltimore harbor in September 1814, the bombardment commemorated in “The Star-Spangled Banner.” She had also been to the Arctic before the Franklin expedition: George Back commanded her in 1836–37 for an Arctic voyage that nearly resulted in her being crushed by ice, requiring heroic effort to bring her back to England in a damaged state.
The conversion of both ships for the Franklin expedition involved installing Maudslay, Sons and Field locomotive steam engines — railway engines, essentially, adapted for maritime use — connected to screw propellers. The engines were of modest power by later standards, capable of moving the ships at perhaps four knots in calm water, and they were intended primarily as a supplement to sail rather than as a primary means of propulsion. But they gave the expedition a capability that purely sail-powered ships lacked: the ability to maintain position and maneuver in conditions where wind was absent or contrary.