The Canon de 27 C modèle 1864 was a 274 mm cast iron rifled breech loader built-up gun used by the French Navy, as coastal artillery, and also in land warfare.

Contrary to the lighter calibers, it was originally meant to be used only as a coastal gun.

In February 1869 a decision was made about the changes to be applied to all guns that dated from before 21 December 1868.

It was made by first removing the frettes (rings) and then boring out the gun and inserting a steel inner tube inside the cast iron barrel.

[8] At the same time, the length and diameter of the powder chamber of the 27 cm gun were increased.

In calibers it was L/16.6, which was a step down compared to the length of the 16, 19, and 24 cm guns, which were all about L/19.

It consisted of puddle steel rings that were shrunk over the barrel, putting pressure on it to make it more resistant.

[12] The vent of the cannon entered the chamber 610 mm from the rear of the gun.

Groove No 1 differed from the others and connected to a channel (rigole) in the chamber that guided the projectile to its proper position.

This meant more grooves, different obturator, ignition throught the breech etc.

[8] The 27 cm M 1864 gun fired a regular grenade called Obus oblong en fonte.

[14] There was also a grenade of chilled cast iron called obus oblong en fonte dure.

It carried an internal explosive charge of 2.5 kg, which was ignited by the heat of the impact.

There was also a boulet ogival en fonte, which was a bit a longer, so it attained the same weight.

There was also boulet ogival en fonte dure which was the almost the same as the exercise shot, but was obviously meant to be used in combat.

The boulet cylindrique en acier was meant for combat at the closest distances.

The frame had little rollers that could move it sideways, allowing the gun to be aimed horizontally.

[21] The battery carriages for the 27 cm gun were by themselves big machines.

[22] The big difference between the battery carriage and the semi-turret carriage for use on the upper deck, was that the latter put the trunnions 2.05 m above the ground, allowing an elevation of 32.3° and thus much longer range.

It could then be moved sideways while it rolled on four little wheels that fit into a rails (circulaire).

[26] The dimensions of the 1870 model carriage were: 6.25 m length, 2.45 m wide and 3.00 m high.

The ironclad Océan had four 27 cm guns in its armored citadel and four Canon de 24 C modèle 1864 above it in semi-turrets.

In May 1891, four platforms for 27 cm modèle 1864-1866 guns were tested at Fort Saint Louis in Martinique.