Ballistic-evaluation and proof-test data were obtained for 4-in. rockets fired from a production model Mk 19 Mod 0 launcher, a subcaliber launcher for the Mk 108 antisubmarine rocket launcher. The Mk 19 tube and spacer assemblies were inserted into the Mk 108 guide tube. Seven 6-round salvos were fired at 0 deg train and elevation. A simultaneous firing of 2 rounds appeared to be caused by a surge or voltage drop which permitted the stepper switch to cycle. Two normal salvos were fired with the Mk 19 circuit alone. Six salvos fired properly at train angles of or - 30 deg with the original test arrangement and a positive contact between the firing-circuit source and the spacer-tube firing lead. The tests indicated that dual firings occurred at train angles between or - 30 deg because only 1 of the Mk 108 firing pins was operative and any 2 adjacent rockets could fire simultaneously. At 35 deg train angles, both pins were operative and normal firing occurred. The ballistic data showed an excessive yaw and dispersion in the 4-in. rockets. Recommendations were made that 1 the Mk 108 be trained 35 deg before loading the Mk 19 into the guide tube 2 the Mk 108 firing pins be checked for contact and 3 the 4-in. rocket be modified to improve flight and decrease dispersion.