The Evolution of French Battleship Protection Schemes 1900–1910

The recently-completed Courbet departs Toulon in January 1914. She is flying the flag of Vice-Admiral Boué de Lapeyrère, C-in-C of the Armée Navale.

Courbet departing Toulon in the Spring of 1914. The broad white band on the first funnel marks her out as the lead ship of the 1st Division of the elite 1st Battle Squadron.

The Evolution of French Battleship Protection Schemes 1900–1910

The reintroduction of a substantial medium QF battery meant that the simplified protection system of the Patrie and Danton classes, in which the ammunition trunks of the turrets rose above the ‘citadel’ as isolated armoured cylinders or cones and the single casemate guns were in independent armoured redoubts (see accompanying schematic), had to be drastically modified.

Eighteen of the 22 battery guns were housed within a large armoured casemate on the 1st deck which extended from the sides of the barbette of turret 1 to just aft of amidships, embracing the working chambers and ammunition trunks of the two wing turrets. The remaining four guns were in a casemate on the main deck, between the barbettes for the two after turrets. The casemates themselves were protected by thick walls of cemented plates which extended at their full thickness down to the main belt, so that the larger of the two casemates formed an ‘upper citadel’ amidships.

The other modification to the earlier Patrie/Danton scheme was that some of the layered protection amidships previously applied uniformly to the main deck was moved upwards to form the roof of the casemates, which now constituted extended armoured boxes above the citadel.

Protection of the hull and machinery was on a similar level to the Danton class. The two-strake belt, which was of cemented plates with a maximum thickness of 250mm, extended from the bow (Frame 165) to Frame 2, where it was closed by a transverse bulkhead of 180mm cemented armour. It was 4.05 metres high, with 1.7m being beneath the waterline at normal loading, and was steadily reduced in thickness to 160mm at the ends. In a break with previous practice, there was no light upper belt of special steel (cuirasse mince) forward of the main casemate, and the 160mm forward and after walls of the latter, which were two decks high and extended down to the main deck, formed the transverse bulkheads against enfilading fire.

The caisson cellulaire behind the belt retained the cofferdam which was a feature of earlier ships, comprising watertight cells a single frame in length directly behind the outer hull plating. However, the passageways immediately inboard of the cofferdam were suppressed in favour of a single broad central passageway and a system of tight compartmentation outboard of it. Virtually all the compartments outboard of this central passageway served as coal bunkers.

The protection scheme for the Dantons was essentially the same as for Liberté, with continuous layered protective decks above and below the entrepont cellulaire, and every key item above the main deck (turrets, casemates, conning tower) treated as an armoured ‘island’. Note also in the drawings of Liberté and Danton the light upper belt of special steel forward, and the armoured transverse bulkhead abeam 30cm turret 1 to protect against enfilading fire.

Courbet marked a complete break with earlier practice. The main QF battery and the after casemate guns were in boxes of 160mm cemented armour above the citadel, and the upper armoured deck was broken to provide protection to the roofs of the casemates. There was no separate upper belt of special steel forward.

The main and after casemates, which extended the full width of the hull, were protected by plates of 160mm cemented armour secured to a double thickness of 10mm plating; only the curved plates of the cylindrical gunshields were of special steel. There was the same level of protection for the end bulkheads as for the sides. Outboard of the wing turrets on either side of the ship there were two large cemented plates 232mm thick which provided additional protection for the working chambers and ammunition trunks.

The protected decks were on the built-up principle which characterised earlier French battleship construction, using two/three layers of mild steel steel on the flat, and replacing the upper layer by thicker plates of armour-quality ‘special’ steel on the slopes to provide a back-stop for shells and splinters which penetrated the upper belt. The lower armoured deck (1st platform deck), which was just above the waterline, was continuous, and comprised three layers of mild steel with a total thickness of 40mm (12/14/14mm); the upper (12mm) layer was replaced on the slopes by plates of 42mm special steel for a total thickness of 70mm. However, the upper armoured deck (main deck) had layered protection only fore and aft of the main casemate, comprising three layers with a total thickness of 48mm (12/18/18mm), reducing to two layers 30mm thick (12/18mm) at the bow and stern. This deck was effectively raised amidships to form the roof of the main casemate, which comprised two layers with a total thickness of 40mm (15/25mm).

The 30cm turret armour comprised five plates of 250mm cemented armour on the face and sides, secured to a double thickness of 20mm steel; the rear wall, intended to counterbalance the weight of the guns, comprised two plates of 360mm mild steel with a similar backing. The roof comprised three layers of 24mm steel, and the turret floor a single thickness of 60mm special steel on a double layer of 20mm; the rangefinder hood for the turret/section commander and the rangetaker was of 200mm cast nickel steel.

The ring bulkheads for the end turrets were protected by 236mm cemented plates on a double thickness of 17mm steel. This was generally reduced to 56mm special steel inside the casemates, although the outboard sides of the ring bulkheads for the wing turrets were reinforced to 116mm and were connected to the outer wall of the main casemate by angled bulkheads of 130mm special steel.

The conning tower was virtually identical in its configuration and protection to that of the Danton class.

The Courbets were France’s first dreadnoughts. They constituted a break with earlier construction not only by virtue of their uniform all-big-gun armament but also in terms of their size: they were fully 20 metres longer than their immediate predecessors of the Danton class and had a displacement 25% greater. They had a new hull form and a radically different layout. They also featured a powerful dual-purpose battery of medium-calibre QF guns capable of both supplementing the main guns and engaging enemy destroyers.

Given the novelty of the design, it is unsurprising that there were defects which became quickly apparent once the ships entered service. Sea-keeping would have been much-improved had only a single turret been mounted on the forecastle, as in their British and German counterparts. The restricted elevation of the main guns would prove to be a major issue: the design of the turrets permitted a maximum elevation of 12 degrees, whereas 15 degrees was standard for contemporary foreign dreadnoughts, and in the latest British ships it was 20°. Firing the new heavyweight shell, the 30cm guns could range only to 13,500m. When the Courbet class was designed the French thought it inconceivable that future battle ranges would exceed 10,000m due to the difficulty of providing effective fire control. Moreover, the new ‘all-big-gun’ ships were intended to fight alongside the battleships of the Danton class, which would be completed only during the second half of 1911 and would remain first-line units for many years to come, not to supersede them. It was therefore a considerable shock to the Marine Nationale when the early actions of the Great War, and in particular the Battles of the Falkland Islands and Dogger Bank, saw ranges of engagement of 14,000–17,000 metres.

These failings would be addressed in future years, but due to the pressures of war it would be the 1920s before the ships were subjected to a radical reconstruction which focused on extending gun range and on corresponding improvements in fire control. As it was, despite British influences on the design, the dreadnoughts of the Courbet class remain essentially French in conception.

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