Hilsea Lines - The Current Lines

The Current Lines

The current lines were constructed between 1858 and 1871. They included special fortified bridges for road and rail access. A model of the Hilsea Lines featured in the 1862 International Exhibition. Even before their completion the Hilsea Lines had been rendered obsolete by the 1859 Royal Commission and advances in artillery technology. The development of rifled artillery meant that it was now possible for an enemy to occupy the high ridge of Portsdown Hill north of Portsmouth and shell the naval base from several miles away without having to attack the Hilsea Lines. To counter the new threat a series of "Palmerston Forts" were constructed on Portsdown Hill and the Hilsea Lines were scaled back. In particular a pair of forts that it had been planned to place behind the lines were not constructed.

As completed, the lines are largely built from clay and chalk and were 30 feet (9.1 m) high when completed. Traffic on the London Road passed through the lines via a pair of 15-foot-wide (4.6 m), 18-foot-high (5.5 m) tunnels. There was also an 8-foot-wide (2.4 m), 11-foot-high (3.4 m) tunnel for pedestrians. The section containing the tunnels was demolished in 1919.

Then a further tunnel through the lines was provided for the railway. Finally, a 6-foot-wide (1.8 m) and 8-foot-high (2.4 m) tunnel was built through the West centre curtain to act as a sally port.

It was originally planned to equip the lines with smoothbore guns; however, it appears the guns may never have been fitted. In 1886 the lines were equipped with a mix of RML 7 inch guns and RBL 7 inch Armstrong guns on Moncrieff mountings fitted in newly constructed concrete emplacements. Further RBL 7 inch Armstrong guns were fitted in the original casements. The guns were removed in 1903. A small number of guns were mounted on the lines during World War II.