Flower Class (1940) Corvette

During 1938-39 as WW2 war clouds gathered, an appraisal was done for convoy escort vessels especially for the numbers needed and available. It was obvious that there was a great shortage of hulls available.

To meet this shortage a more simple design of convoy escort was needed which non-specialist warship builders could construct, and which would not use fire control systems and turbine machinery which were already capacity limited.

It was anticipated that convoys would only require escort from the Western Approaches to around the British Coast. So the length was kept down to about 200ft. Less than the 300ft minimum required for ocean escorts, but sufficient for coastal work. These smaller hulls could also be constructed in yards whose slips were too short for 300ft vessels. 

The hull form was based on that of a whaler, which would allow a speed of 16kts. The minimum needed for an escort. The whaler hull form was faster than the alternative trawler hull form.

The power plant of single screw reciprocating machinery was a practical solution as it was a type of installation reserve personnel would be more familiar with than the more powerful turbines. It was also the only type of machinery available in any quantity in the time needed.

They were intended for operations in coastal and adjoining waters but the term coastal escort was considered unsuitable. So they were given the new classification Corvette.

Under the 1939 Estimates 56 units were ordered. Then following the outbreak of war another 60 units were ordered in the UK, and 50 in Canada under the 1939 Emergency Programme. Smaller additional orders were placed in 1940, 41 and 42.

In addition the French Navy ordered 4 units pre-war and 18 more later in 1939. Sixteen to be built in the UK and six in France. Of the initial order of four, the lead ship was mined during trials, and of the remaining three, none were completed before the French surrender. They were taken over by the Royal Navy. Of the second order none of the 16 to be built in the UK had been started when France surrendered. Of the six under construction in France, they were captured incomplete, and finished for the German navy as PA1 - PA6. All were lost during the war.

In all a total of 300 Corvettes were ordered:
164 constructed in the UK, (16 for France);
130 constructed in Canada, (25 for the USA under lend/lease);
16 constructed in France.

With the fall of France U-boats could sortie much further out into the Atlantic. So convoys needed escort much further out into the Western Approaches. Eventually right across the Atlantic. 

So the Corvettes were forced to operate in heavier seas and at longer ranges beyond their design capabilities. They did not prove ideal ocean escorts. But they and their crews did valiant priceless duty when there was no alternative available.

Transfers to allied navies included;
1 to Belgian Navy;
9 to free French Navy;
6 to Royal Norwegian Navy;
1 to Royal Netherlands Navy;
4 to Royal Hellenic Navy;
1 to Royal Yugoslavian Navy;
10 to the US Navy during 1942. To meet their severe shortage of escort vessels. (In compensation 10 were ordered from Canadian yards under lend/lease. On completion these were first transferred to the Royal Navy and then loaned to the Canadian Navy).

Six units under construction in the Harland and Wolff (Belfast) yard were cancelled 23-Jan-1941 after yard facilities were damaged during an air raid.

Overall the Flower and later, Modified Flower Corvettes were recognised as being a very crude and basic way of taking an Asdic Set, depth charges and a 4in gun into action. But they were the only way to quickly get hulls into the water to provide a degree of convoy escort during the critical years 1940-43. They and their crews continued to provide great service up until the end of the WW2. 

The hard won lessons were incorporated into the Castle Class (1943) Corvettes and the new larger and more capable Frigates.


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This page last edited - 01 March, 2013.

Copyright Ian M King, except where otherwise indicated.