France wanted to use submarines for maintaining communication with her colonies in wartime according to the Dutch magazine Marineblad dated 1921

An item referred to the Naval and Military Record dated 17 January 1913 in which an article was published dealing with the strengthening of the French submarine fleet. It reported that as an experiment in 1924 2 fast 2.700 ton submarines were to be laid down with a heavy artillery armament and torpedo tubes. The designers wanted to protect the colonies with such submarines, an ides which was by naval experts discussed. Merchant submarines of 3.500 ton and mail boat submarines of 6.000 ton were mend to maintain the communication with the French colonies Algeria, Senegal, Congo and Madagascar. Several engineers made designs for this kind of submarines. While France was not able to conqueror superiority at sea with her surface warships were the communication under water or in the air of the utmost importance. 

French steam river boats to be used in French Congo according to the magazine Mitteilungen aus dem Gebiete des Seewesens dated 1889 no. 1-2

An item reported that by M. Paul Oriolle, Nantes, France 4 steam boats were ordered to be in the Congo (1) with the dimensions 15 x 3 metres. One of the boats was already completed and achieved the trials without success. With a natural draft and wood fired was the speed 14,58 knots due to the improved Oriolle boiler.

Note
1. French Congo was a protectorate since 10 September 1880, formally established on 30 November 1882, confirmed at the Berlin Conference of 1884-1885 and became in 1910 French Equatorial Africa of which also Gabon formed part.