 At the advent of World War II , the Royal Canadian Navy greatly desired to build naval class warships . However , Canadian ship building yards were not capable of building such vessels and at the time it was impossible to buy such ships from Britain as its capacity was taken up entirely by its own defence needs . It was decided that a modified whale catcher design could be built by Canadian yards which could later be traded with Britain for Tribal @-@ class destroyers . The barter scheme eventually failed , but the Canadian Navy had already ordered the whale catchers . Sixty @-@ four ships were originally ordered and these were built between 1939 – 1940 , becoming the basis of the RCN corvette fleet . 
