On the subject of the Flower class corvette, in his book ‘Atlantic Escorts’ Brown lists the following options that were looked at for a cheap A/S vessel.
Conversion of commercial trawler. About 620 tons, 11–12 knots. Coal burning, cylindrical boiler and single reciprocating engine. Endurance about 3,500 at 9 knots. Complement 24. They were moderate asdic platforms but had inadequate subdivision. Conversion would take 4 weeks and cost £35,000.
Admiralty trawler. 510 tons. 11¾–12½ knots. Coal burning, cylindrical boiler and single reciprocating engine. Endurance 3,500 at 9 knots. Complement 24. Good asdic platform with adequate subdivision. They would take 4 months to build and cost £57,000.
Converted whale catcher (Southern Pride). 700 tons, 16 knots. Oil fuel, two boilers, one reciprocating engine. Endurance 4,000 at 12 knots. Complement 30. Moderate asdic platform, subdivision bad. Conversion would take 6 weeks and cost £75,000.
New whale catcher to Admiralty requirements. 900 tons, 16 knots. Oil fuel, two boilers, one reciprocating engine. Endurance 4,000 at 12 knots. Complement 30. Good asdic platform with adequate subdivision. They would take 7 months to build and cost £90,000.
A/S version of Bangor. 500 tons, 17 knots. Oil fuel, two boilers, turbines (alternative diesel). Endurance 4,000 at 10 knots. Complement 50. Good asdic platform and good subdivision. They would take 8 months to build and cost £135,000.
Simplified Guillemot. 580 tons, 20–1 knots. Oil fuel, two boilers, geared turbines. Endurance 3,000 at 11 knots. Complement 63. Good asdic platform and good subdivision. They would take 8 months to build and cost £160,000.
Hunt class. 890 tons, 29 knots. Endurance 3,500 at 20 knots. Oil fuel, two boilers, geared turbines. Complement 144. Good asdic platform and good subdivision. They would take 12 months to build and cost £400,000.
It was noted that all would be ‘seaworthy craft capable of hard work’ but not equal. Similarly they were ‘vessels in which men can live in reasonable conditions’ but again not equal. Protection depended on transverse subdivision and the commercial trawler and whale catcher were ‘very unsatisfactory’ in that regard. Time and cost figures are relative. Note the cost of Guillemot, far larger than usually quoted. Faced with these figures, the Board chose option 4, which developed into the Flower class – and who can blame them?
The problem was still seen, particularly in respect of coastal work on the east coast. The little coastal sloops of the Kingfisher class were capable – and beautiful – but rather shallow for asdic work and far too expensive (Kingfisher cost £160,000) to build in numbers. They displaced 550 tons, coming under a clause of the London Treaty permitting unrestricted building of vessels under 600 tons. Trawlers, particularly those of Admiralty design developed from Basset, were cheap and useful but their speed of twelve and a half knots and short endurance limited their ASW capability, as did their size. Something bigger but still cheap was needed.
It seems that ideas were sought from several builders but details have only survived for the successful candidate from Smith’s Dock. This was a well-known shipbuilder on the Tees specialising in fishing vessels and most notable for its whale catchers. Their managing director, Mr W Reed, pointed out that they had been building A/S vessels since the ‘Zed’ whalers of 1915, followed by the ‘Kil’ class boats, also of World War I. These ‘Kils’ were originally intended to have oil-fired, water-tube boilers for a speed of seventeen to eighteen knots, remarkably similar to the Flowers of World War II. However, oil was scarce, as were skilled personnel, and they completed with coal-fired Scotch-type boilers and a speed of fourteen knots.
Reed’s first proposal in 1938 was based closely on the whale catcher Southern Pride, lengthened by thirty feet. There was a meeting in January 1939 at which Reed seems to have been given some degree of approval for a 700-ton ship costing £90,000. It then grew to 1,390 tons, mainly as a result of a change to coal burning. Fortunately, sanity returned and final approval was for an oil burner of 940 tons (standard). The DNC (Sir Stanley Goodall) was an enthusiastic supporter of the proposal, noting in his diary, ‘I spoke against Guillemot and for whale catcher.’12 Initially they were known as ‘patrol vessels of whale catcher type’. The origin of the term ‘corvette’ is unclear; it is often said that Churchill chose it and this may well be true, though no evidence has been found to support this. Canadian sources attribute it to Adm Nelles, RCN. Both could be right. Historically it was a very unsuitable name, as a corvette was much bigger than a sloop, but it had a fine ring to it.
At a meeting on 8 February 1939 Messrs Edwards and Reed of Smith’s Dock drew attention to the performance of the steam trawler Imperialist, which they would guarantee for thirteen knots loaded with 1,050ihp (indicated horsepower) on wet steam. DNC was not interested, as the extra speed was little more than the Admiralty design for which Smith’s Dock were doing the drawings and the Admiralty design was easier to build. DNC was more interested in the whale catchers Southern Pride and Sondra. The drawbacks to these were poor subdivision and the bar keel. Reed thought he could produce an intermediate design with speed of fifteen to sixteen knots. It was agreed that he should look into the possibility and send an outline drawing and particulars of dimensions, speed and draught, and state time to build, cost and breakdown of equipment between ASI/commercial.
Dr Harland has pointed out that the Flowers were far from a copy of the Southern Pride. They had a flat plate keel instead of the whale catchers’ bar keel. Corvettes had bilge keels, inadequate in size at first. They were given a pair of stockless anchors and a windlass. A forecastle was added, forming a seamen’s washplace, heads and stores. The mess deck was below and traditionalists were horrified that seamen and stokers messed together.
The bridge block was sited above the wardroom and two officers’ cabins. On the lower level there was the CO’s cabin and the officers’ bathroom, with a wheelhouse above. On top there was an open bridge with an enclosed compass shelter. In early years there were many individual variations in bridge details but later most were altered to a standard design. The POs’ mess was aft with the galley above, ensuring that food was cold before it reached the forward mess deck.
It was originally thought (1939) that these ships could be used to enforce the blockade on the Northern Patrol. To this end they were given a long-range radio that required two masts some distance apart. Six RN corvettes completed with the two-masted rig but many more retained the foremast ahead of the bridge, where it interfered with the view ahead. All early RCN ships had two masts.
The machinery was little changed from Southern Pride, a four-cylinder, triple-expansion engine driving a single shaft. Such engines were simple to build and within the capability of the engineering departments of most shipyards. Smith’s Dock supplied patterns to other builders and a total of 1,150 units were built for corvettes, frigates and transport ferries (LST 3). Shaft rpm was increased to 185, about the limit for a reciprocating engine lacking forced lubrication. At this speed the engine developed 2,750ihp giving a ship speed of sixteen knots, much faster than any trawler but less than a surfaced U-boat. The machinery was generally reliable, though the maintenance task was heavy. There were early problems with crankshaft alignment, which led to some bearing failures. The majority had two Scotch-type boilers but those from Harland and Wolff had Howden Johnson units, and about twenty later ships (mostly Canadian) had water-tube boilers in closed stokeholds. The particulars of these war-winning engines were: stroke 30in; high-pressure diameter 18½in; medium-pressure 31in; both low-pressure 38½in.