Heugh Gun Battery was built on Hartlepool Headland from 1859, when fears of a French attack on the British mainland were rife. Nine guns were placed in three locations, though not all emplacements remain. The original guns had a range of about a mile and a half, but were never fired in anger.
In the 1880s and 1890s the weapons were upgraded, then at the turn of the century a major overhaul of the whole site took place with substantial restructuring in concrete – most of which remains today. The new guns which were fitted at this time had a range of over seven miles and, thanks to the uncertainties of 20th century international relations, were kept primed until the mid 1950s.
In 1914, they became the only British mainland guns to engage a 20th century enemy when they exchanged blows with German warships who were having a pop at the nearby town. During WWII, the guns were upgraded again, doubling their range, but were never used. Eventually, the defences were, of course, rendered useless by the development of long-range nuclear missiles, and the battery was closed in 1956.
[Information taken from the Heugh Battery Museum website]