The Marshal Ney and the Marshal Soult were monitors, constructed at Palmer's Shipyard in Jarrow between January and November 1915. Monitors were small ships intended for shore bombardment, and were thus heavily armed for their size. Soult and Ney were armed with a single twin 15in turret, freed up by the decision to turn Repulse and Renown from battleships with four such turrets to battlecruisers with three. Other British monitors were armed with 12in or 14in guns.

The first monitors to be used by the RN during WWI were three lightly armed river monitors, being constructed for Brazil in British yards in 1914. These three were requisitioned and (somewhat naturally given their role), given the names of British rivers - Humber, Mersey and Severn. The first to be constructed by the RN during the war were the Abercrombie class. The genesis for this class came following a visit to the UK by Charles M Schwab, president of the Bethlehem Steel Corporation. His company had been building four twin 14in turrets for a battlecruiser being built in Germany for Greece. With the British blockade of Germany in place, there was no chance that this ship would be completed, and Schwab sold the turrets to Britain to recoup his investment. Following a very quick, simple, design study, four monitors were put into construction. Initially, these ships were to be named after figures from the American Civil War, commemorating the origin of the turrets (and of the namesake of the type) - Ulysses S Grant, David Farragut, Stonewall Jackson and Robert E Lee. However, the Americans pointed out that this might be politically tactless given American neutrality. As such, they were renamed after British generals. The next class, the Lord Clives, used turrets taken from decommissioned British battleships, and were named from the start after British generals. The two Marshals came next. They were named after French generals of the Napoleonic period as a way of paying tribute to France's contributions to the war. While British ships could not be named after American figures for fear of showing an inappropriate closeness between a neutral power and a belligerent, the same argument did not apply between two allies.

Beyond the monitors, few other British ships have been named after British generals (Iron Duke is about the only exception), let alone foreign ones. These ships were named, near uniquely, for French generals, as a way of fostering closeness between the Allies.

Sources:

Big Gun Monitors: Design, Construction and Operations 1914-1945, Ian Buxton, Seaforth, 2012

Warrior to Dreadnought: Warship Design and Development 1860-1905, David K Brown, Seaforth, 2012