On 27 February 1856, Coles was made captain.
He was placed on half pay after the war ended and spent his time creating designs for turret ships.
Up to this time the principal armament of warships had been batteries of guns firing from fixed ports in the sides of the ship.
On 10 March 1859 he filed a patent for a revolving turret, although it is not clear how he came by the idea.
The American USS Monitor, constructed by John Ericsson in 1861, incorporated a revolving turret and Ericsson claimed the idea of a revolving protected gun was an old one.
The Times suggested that Marc Brunel had given Coles the idea.
Coles' design aim was to create a ship with the greatest possible all round arc of fire, as low in the water as possible to minimise the target.
This proved to be a weakness in designs he created, because he was unwilling to compromise these aims for the practical necessities of sailing ships' rigging, decks sufficiently high to be clear of heavy seas and other necessary superstructures which restricted the guns' rotation.

The Admiralty accepted the principle of the turret gun as a useful innovation, and incorporated it into other new designs.
However, they could not accept his other ideas on ship design.
Coles submitted a design for a ship having ten domed turrets each housing two large guns.
The design was rejected as impractical, although the Admiralty remained interested in turret ships and instructed its own designers to create better designs.
Coles submitted his plans to anyone who might be interested and succeeded in enlisting a number of supporters, including Prince Albert, who wrote to the first Lord of the Admiralty, the Duke of Somerset, supporting the construction of a turret ship.
In January 1862, the Admiralty agreed to construct a ship, HMS Prince Albert, which had four turrets and a low freeboard, intended only for coastal defence.
Coles was allowed to design the turrets, but the ship was the responsibility of the chief Constructor Isaac Watts.

Coles had another proposal, to take an existing timber ship, remove its upper decks and existing broadside guns and replace them with four turrets on a flat deck.
The ship was also to be fitted with 5.5 inches (140 mm) of armour in a belt around the waterline.
HMS Royal Sovereign was completed in August 1864, ahead of Prince Albert.
Like Prince Albert it had only minimal sails intended to steady the ship rather than drive it along at any speed.
The low freeboard was countered by hinged sections increasing the height of the sides above the deck; these were dropped down to allow the guns to fire.
Coles later took command of Royal Sovereign for the July 1867 Naval Review.

While these ships were building, Coles made further proposals which the Admiralty resisted pending completion of the trial ships already under construction.
However, once Royal Sovereign was completed and had received favourable reports, he requested Admiralty assistance in creating a new design.
This was to be based upon the existing HMS Pallas designed by the new Chief Constructor, Edward Reed.
The Admiralty provided the original plans of the ship plus Joseph Scullard, constructor at Portsmouth dockyard, to assist.
The resulting single turret design was rejected, but the Admiralty instructed Reed to create a larger version with two turrets which became HMS Monarch, laid down in 1866 and completed in June 1869.
Coles complained at the inclusion of a forecastle and poop which prevented the guns firing fore and aft, and the high position of the guns 17 feet (5.2 m) above water level, but his objections were dismissed.
Reed maintained the features were all intended to improve seaworthiness.
On 27 February 1856, Coles was made captain. He was placed on half pay after the war ended and spent his time creating designs for turret ships. Up to this time the principal armament of warships had been batteries of guns firing from fixed ports in the sides of the ship. On 10 March 1859 he filed a patent for a revolving turret, although it is not clear how he came by the idea. The American USS Monitor, constructed by John Ericsson in 1861, incorporated a revolving turret and Ericsson claimed the idea of a revolving protected gun was an old one. The Times suggested that Marc Brunel had given Coles the idea. Coles' design aim was to create a ship with the greatest possible all round arc of fire, as low in the water as possible to minimise the target. This proved to be a weakness in designs he created, because he was unwilling to compromise these aims for the practical necessities of sailing ships' rigging, decks sufficiently high to be clear of heavy seas and other necessary superstructures which restricted the guns' rotation.
The Admiralty accepted the principle of the turret gun as a useful innovation, and incorporated it into other new designs. However, they could not accept his other ideas on ship design. Coles submitted a design for a ship having ten domed turrets each housing two large guns. The design was rejected as impractical, although the Admiralty remained interested in turret ships and instructed its own designers to create better designs. Coles submitted his plans to anyone who might be interested and succeeded in enlisting a number of supporters, including Prince Albert, who wrote to the first Lord of the Admiralty, the Duke of Somerset, supporting the construction of a turret ship. In January 1862, the Admiralty agreed to construct a ship, HMS Prince Albert, which had four turrets and a low freeboard, intended only for coastal defence. Coles was allowed to design the turrets, but the ship was the responsibility of the chief Constructor Isaac Watts.
Coles had another proposal, to take an existing timber ship, remove its upper decks and existing broadside guns and replace them with four turrets on a flat deck. The ship was also to be fitted with 5.5 inches (140 mm) of armour in a belt around the waterline. HMS Royal Sovereign was completed in August 1864, ahead of Prince Albert. Like Prince Albert it had only minimal sails intended to steady the ship rather than drive it along at any speed. The low freeboard was countered by hinged sections increasing the height of the sides above the deck; these were dropped down to allow the guns to fire. Coles later took command of Royal Sovereign for the July 1867 Naval Review.
While these ships were building, Coles made further proposals which the Admiralty resisted pending completion of the trial ships already under construction. However, once Royal Sovereign was completed and had received favourable reports, he requested Admiralty assistance in creating a new design. This was to be based upon the existing HMS Pallas designed by the new Chief Constructor, Edward Reed. The Admiralty provided the original plans of the ship plus Joseph Scullard, constructor at Portsmouth dockyard, to assist. The resulting single turret design was rejected, but the Admiralty instructed Reed to create a larger version with two turrets which became HMS Monarch, laid down in 1866 and completed in June 1869. Coles complained at the inclusion of a forecastle and poop which prevented the guns firing fore and aft, and the high position of the guns 17 feet (5.2 m) above water level, but his objections were dismissed. Reed maintained the features were all intended to improve seaworthiness.
Cowper Phipps Coles