Editing French submarine Surcouf (section)

==Design==

The [[Washington Naval Treaty]] had placed strict limits on naval construction by the major naval powers in regard to displacements and artillery calibers of battleships and cruisers. However, no agreements were reached in respect of light ships such as frigates, destroyers or submarines. In addition, to ensure the country's protection and that of the empire, France started the construction of an important [[List of submarines of France|submarine fleet]] (79 units in 1939). ''Surcouf'' was intended to be the first of a class of three submarine cruisers; however, she was the only one completed.

The missions revolved around:
* Ensuring contact with the [[List of French possessions and colonies|French colonies]];
* In collaboration with French naval squadrons, searching for and destroying enemy fleets;
* Pursuing enemy convoys.

''Surcouf'' had a twin-gun turret with [[203mm/50 Modèle 1924 gun|203&nbsp;mm (8-inch) guns]], the same calibre as the guns of a [[heavy cruiser]], provisioned with 60 rounds. She was designed as an "underwater heavy cruiser", intended to seek out and engage in surface combat.<ref>{{cite book |last=Winchester |first=Clarence |year=1937 |title=Shipping wonders of the world |volume=41–55 |publisher=Amalgamated Press |page=1431}}</ref> The boat carried a [[Besson MB.411]] observation [[floatplane]] in a hangar built aft of the [[conning tower]] for reconnaissance and [[Artillery observer|observing fall of shot]].

The boat was equipped with ten [[torpedo tube]]s: four {{convert|550|mm|in|abbr=on}} tubes in the bow, and two swiveling external launchers in the aft superstructure, each with one 550&nbsp;mm and two {{convert|400|mm|in|abbr=on}} [[torpedo]] tubes.  Eight 550&nbsp;mm and four 400&nbsp;mm reloads were carried.<ref>{{cite book |last1=Huan |first1=Claude |year=1996 |title=Le croiseur sous-marin Surcouf  |location=Bourg en Bresse |publisher=Marines editions |pages=53–54}}</ref> The 203&nbsp; Modèle 1924 guns were in a pressure-tight turret forward of the conning tower. The guns had a 60-round magazine capacity and were controlled by a [[Director (military)|director]] with a {{convert|5|m|ft|abbr=on}} rangefinder, mounted high enough to view an {{convert|11|km|nmi mi|lk=on|abbr=on}} horizon, and able to fire within three minutes after surfacing.<ref name=Netmarine-Main/> Using the boat's periscopes to direct the fire of the main guns, ''Surcouf'' could increase the visible range to {{convert|16|km|nmi mi|abbr=on}}; originally an elevating platform was supposed to lift lookouts {{convert|15|m|ft|abbr=on}} high, but this design was abandoned quickly due to the effect of [[Ship motions#Reference axes|roll]].<ref name=Netmarine-Caracter>[http://netmarine.net/g/bat/surcouf/caracter.htm Sous-marin croiseur ''Surcouf'': Caractéristiques principales]</ref> 
The Besson observation plane could be used to direct fire out to the guns' {{convert|26|mi|nmi km|abbr=on}} maximum range. Anti-aircraft cannon and machine guns were mounted on the top of the hangar.

''Surcouf'' also carried a {{convert|4.5|m|ftin|abbr=on}} motorboat, and contained a cargo compartment with fittings to restrain 40 prisoners or lodge 40 passengers. The submarine's fuel tanks were very large; having enough fuel for a {{convert|10000|nmi|km mi|abbr=on}} range and supplies for 90-day patrols.

The test depth was {{convert|80|m|ft|abbr=on}}.

The first commanding officer was [[Frigate Captain]] (''Capitaine de Frégate'', a rank equivalent to [[Commander]]) Raymond de Belot.

The boat encountered several technical challenges:
* Because of the low height of the rangefinder above the water surface, the practical range of fire was {{convert|12000|m|yd|abbr=on}} with the rangefinder, increased to {{convert|16000|m|yd|abbr=on}} with sighting aided by periscope, well below the guns' maximum range of {{convert|26000|m|yd|abbr=on}}.
* The duration between the surface order and the first firing round was 3 minutes and 35 seconds. This duration would be longer if the boat was to fire [[Broadside (naval)|broadside]], which meant surfacing and [[Training (gunnery)|training]] the turret in the desired direction.    
* Firing had to occur at a precise moment of pitch and roll when the ship was level.
* Training the turret to either side was impossible when the ship rolled 8° or more.  
* ''Surcouf'' could not fire accurately at night, as fall of shot could not be observed in the dark.
* The guns' ready [[Magazine (artillery)|magazines]] had to be reloaded after firing 14 rounds from each gun.

To replace the floatplane, whose functioning was initially constrained and limited in use, trials were conducted with an [[autogyro]] in 1938.