The Czechoslovak Army bought three Carden-Loyd tankettes and a production licence for them in 1930, Českomoravská Kolben-Daněk building four copies that same year as prototypes for future orders. The Carden-Loyds were evaluated during the Fall manoeuvres and revealed numerous problems: the crews had very poor vision through the narrow slits, the machine gun had a very narrow field of fire and the crewmen had a difficult time communicating. Furthermore, they were slow, underpowered and often broke down. One of the P-1 prototypes was rebuilt to address these issues with additional vision ports in all directions, internal ammunition storage and the machine gun's field of fire increased to 60°. It was extensively tested during 1931–32 and a few other changes were made as a result. The armor was increased from and from and a fixed machine gun was added for the driver. Two of the other prototypes were rebuilt to the same standard; all three were officially accepted by the Army on 17 October 1933. The order for seventy was placed on 19 April 1933, all being delivered by October 1934. The Škoda T-21 (original designation was Škoda Š-IIc) was Škoda's contribution to the IIc army category (medium tanks for general use) and a direct competitor to Praga V-8-H.