By 1940 the Royal Navy had realized that the s were too small to carry the equipment needed to handle magnetic mines. A bigger ship was designed, ironically about the same size as the older that the Royal Navy had rejected earlier as too large and expensive for mass production. The size of the new ship made them suitable for use as ocean-going escort ships and many were used in that role to fill a critical shortage of escorts. In fact most of the ships built for the RCN were solely employed as such and were fitted with more dedicated anti-submarine weapons than the RN ships. To maximise production, alternate designs were made to use either steam turbines or reciprocating steam engines. This enabled ships to be built at yards more used to merchant ship design, and as with other mass-produced escort vessels (such as the s, or the s, could use merchant-style reciprocating vertical triple expansion (VTE) engines.