French Morocco had from 1912 to 1935 one of the largest gauge network in Africa with a total length of more than . After the treaty of Algeciras where the representatives of Great Powers agreed not to build any standard-gauge railway in Morocco until the standard-gauge Tangier–Fes railway being completed, the French begun to build military gauge lines in their part of Morocco French Morocco.
The 948 km Marrakech–Casablanca–Kenitra–Fes–Oujda line became known as Chemins de fer stratégiques du Maroc and the branch lines diverting from the line as Chemins de fer de pénétration du Maroc. These lines were mostly built during the period of 1921–1925, With the exception of Guercif–Outat Oulad el Hadj–Midelt, which was started in 1916 and completed in 1920.
Casablanca–Boussekoura–Berrechid line
The first French-built narrow-gauge railway was the Casablanca–Bouskoura–Berrechid line, built with portable railway track from Decauville, which also delivered the rolling stock to the line. Construction started in May 1908 and the 52 km line was completed in late July 1908. The trains reached a maximum speed of 20 km/h averaging only 12 km/h between Casablanca and Berrechid.
The locomotives which worked the 500 mm gauge line have not been yet been fully identified. Sources claim: 3 Decauville, / , Bt-n2, built in 1905, delivered new to Touzet, Senegal. 3 Decauville, / , B1t-n2, built in 1907, delivered to Raguet et Heurtematte, Paris.
Chemins de fer stratégiques du Maroc
Casablanca–Marrakech
This gauge line had a short life. It was completed around 1920, activities ceased in 1928.
Casablanca–Boussekoura–Berrechid
This line formed the northern part of the Casablanca–Marrakech narrow-gauge line. In 1913 the French regauged the Casablanca–Berrechid section from to track gauge and was opened to public service in March 1916.
Berrechid–Dar Caïd Tounsi
The Berrechid–Dar Caïd Tounsi (junction) section was completed in 1915 (109 km south of Casablanca).
Dar Caïd Tounsi–Marrakech
The Dar Caïd Tounsi to Ben Guerir section was completed in September 1919. The final section from Ben Guerir to Marrakech was opened in September 1920.
Dar Caïd Tounsi–Mazagan branch
Later also a branch line was built running from Dar Caïd Tounsi, which became a railway junction, to Mazagan (Harbour). This line was opened in early 1928.
Casablanca–Kenitra–Fes
The French started also to build gauge railway north of Casablanca. Rabat 89 km and Port Lyautey -now Kenitra- 128 km was reached in 1913. The opening dates of this line were: Casablanca–Fedala, March 1912, narrow gauge closed in April 1925. Fedala–Rabat, December 1912, narrow gauge closed in April 1925. Rabat–Kenitra, April 1913, narrow gauge closed in April 1923. Kenitra–Meknes, June 1914, narrow gauge closed in May 1923. Meknes–Fes, July 1915, narrow gauge closed in September 1923.
Oujda–Fes
At Kenitra (Port Lyautey) the "main line" turned towards east, the main target for the French military was a rail connection with their Algerian Railways at Oujda, where the French military had built from the Algerian side an 87 km gauge line from Tlemcen via Marnia. This Chemin de Fer de Marnia a Taourirt was completed by 1911.
The 364 km line from Oujda to Fes was difficult to build. The railway had to go over a narrow passage between the Rif mountains in the north and the Atlas in the south. The railway line had to be built with steep gradients and sharp curves to reach – from both sides – the Touahar Pass.
East of Fes the narrow-gauge line followed the route Fes–Sidi Abdallah–Col de Touahar–Bab Marzouka–Taza–Kasba Msoun–Guercif (with branch to Midelt)–Chreia–Taourirt–El Aioun–Naima–Oujda.
Construction started simultaneously from both Fes and Oujda. When the gauge line was completed, it was then possible to travel by train from Morocco to Algeria and Tunisia over the standard-gauge Chemins de fer l´Ouest Algerien.
The French source gives opening dates for sections of Oujda–Fes line: Oujda–El Aioun, December 1912, narrow gauge closed in January 1932. El Aioun–Taourirt, April 1913, narrow gauge closed in January 1932. Taourirt–Guercif, August 1913, narrow gauge closed in January 1932. Guercif–Taza, July 1915, narrow gauge closed in May 1933. Taza–Col de Touahar, July 1918, narrow gauge closed in May 1933. Col de Touahar–Sidi Abdallah, May 1918, narrow gauge closed in April 1934. Sidi Abdallah–Fes, July 1921, narrow gauge closed in April 1934.