of the firing pin. After much trial and error, percussion grenades were abandoned, with the exception of the Citron-Foug, because of their dangerous use. In 1916, Citron-Foug percussion grenades and F1 grenades were adopted in defensive combat phases. In offensive combat mode, short-range explosive OF grenades, suffocating grenades, incendiary grenades and smoke grenades model 1916 were preferred. At the end of 1915, the first trials of the Viven-Bessières rifle grenade began. In 1916, this weapon was in general issued: the use of a cup discharger at the end of the rifle and a balle D propulsive cartridge made it possible to send the grenade (475 grams, including 60 grams of explosives) in good safety conditions to 190 metres. It is then possible to produce a barrage during a defensive phase, to destroy battlements during harassment battles or to reach hidden machine guns during offensive phases. Trench Mortars At the beginning of World War I, the German Army had a stockpile of 150 mortars, which was a surprise to the French and British. The French were able to use modèle 1838 Coehorn mortars dating from just after the Napoleonic Wars, some of which were lent to the British. The Mortier de 58 T was hastily developed at the start of the war. From February 1915 onwards, the high-powered trench mortars were entrusted exclusively to the artillery (organised in batteries of twelve pieces), while the low-powered ones were left to the infantry. The Centre d'instruction de l'artillerie de tranchée (CIAT) was created the same year in Bourges. Given the contempt of the other artillerymen for these units, the personnel assigned to the trench artillery (TA) initially included convicts with suspended sentences from courts-martial coming from all the branches of the army. Later in the war, having ordered 1000 examples in July 1917, the French improved upon the design of the British Stokes Mortar. Further development of the mortar and improved ammunition that continued into the inter-war period would lead to the Brandt Mle 27/31. In September 1917 the French under-secretary of state for inventions sent a circular letter requesting inventors to design a better projectile for the successful Stokes mortar, and Brandt scaled his 60 mm projectile up to 81 mm. Both British and French military adopted the scaled-up design except for the grooves (apparently, their importance wasn't realized at the time) in 1918 as projectile BM (Brandt-Maurice) modèle 1918 (later simplified