Surface ships usually used ASDIC (sonar) to detect submerged submarines. The British corvette, , located the U-boat with ASDIC (sonar). ASDIC (also known as SONAR) was a central feature of the Battle of the Atlantic. Research on ASDIC and underwater sound was expanded in the UK and in the US. They were equipped with radar as well as asdic. The refit lasted until 20 April 1938 and included the installation of ASDIC. Mk V AA gun and a Type 128 Asdic system was installed. In addition, RCN vessels were incapable of operating gyrocompasses, making ASDIC attacks more difficult. ASDIC was effective only at low speeds. Hedgehog solved one of the most pressing problems, keeping ASDIC contact at short ranges. The British tested their ASDIC on in 1920 and started production in 1922. The British tested their ASDIC on in 1920, and started production in 1922.