The first class to use the JA classification were a group of 3160 gallon water tankers built on the 30'-0" standard bogie chassis as shown in the WAGR outline diagram above.

In 1899 six U class wagons (2981, 2987, 2988, 2990, 2993, 2998) and ten R class wagons (3521-3530) were fitted with large rectangular water tanks and classified FB. Some lasted just long enough in this form to be reclassified J in 1900 as 1981, 1988, 2993, 2998, 3521 and 3523-3530 were converted to class U in 1900. The other three wagons (2987, 2990, 3522) became class R in 1901.

In 1908/9 the tanks were re-used when U class wagons 2982, 2998, 3200, 3206, 3213, 3214, 3249 and 3527 were fitted. These conversions lasted rather longer. In 1916 number 3527 was converted to a class Q with 3200 being similarly converted in 1922. In 1923 2998 reverted to class U as did 3206 and 3213 in 1924 and the remaining wagons (2982, 3214 and 3249) in 1925.