attempted to introduce a mezzo-soprano saxophone in the key of F and the "Conn-o-sax", a saxophone-English horn hybrid, but these instruments were soon discontinued after disappointing sales. In 1928, under the direction of Carl Greenleaf's son Leland Burleigh Greenleaf, C. G. Conn opened its Experimental Laboratory, which was unique in the industry. Under Leland Greenleaf's directorship, the department developed the first short-action piston valves (1934), and the 'Stroboconn' (1936), the first electronic visual tuning device. It also developed the "Vocabell" (1932), a bell with no rim, which C. G. Conn described as "vibrat[ing] freely and in sympathy with the vibrating column of air in the instrument," C. G. Conn also developed the "Coprion" bell (1934), a seamless copper bell formed by directly electroplating it onto a mandrel. Under Greenleaf's saxophone specialists Allen Loomis and Hugh Loney, C. G. Conn's research and development resulted in the designs of the 6M alto (1931), 10M tenor (1934), and 12M baritone (1930). The 12M baritone was the first saxophone with both bell keys on the right side, followed by the King Voll-True II (1932) and Selmer Balanced Action (1936). The 6M alto featured an innovative double socket neck that eliminated the large collar on the body tube at the neck joint for a more positive seal and even response, later adopted for King altos and tenors. From 1935 through 1943, C. G. Conn produced the 26M and 30M "Connqueror" alto and tenor saxophones, featuring screw-adjustable keywork and improved mechanisms for the left hand cluster. The keywork was the most fully adjustable of any saxophone during that period. C. G. Conn's laboratory was expanded into the Division of Research, Development and Design in 1940, directed by Earle Kent. C. G. Conn's combined abilities in close-tolerance manufacturing and electronic devices made them a valuable resource for wartime production. From mid-1942 to 1945, C. G. Conn ceased all production of musical instruments for civilian use to manufacture flat & mounted compasses, altimeters, gyro-horizon indicators, and other military instrumentation. A special application of C. G. Conn's "Coprion" process—creating seamless brass bells by depositing copper on a mandrel—was to manufacture silver bearing inserts for the Wright Cyclone airplane engines. In winter 1946-47, production was again interrupted, by a 15-week labor strike. The loss in sales from those disruptions and increased competition from other manufacturers such as Selmer (Paris) and King (H. N. White) caused a serious decline in C.