The Loch Class Frigates


Anything but graceful: showing crude finish & boxy shape designed for war production, here is HMS Loch Fada in 1944.

The Loch class frigates and their associated weapon system were the first design to incorporate both a full understanding of the requirements of the Battle of the Atlantic and the capacity of wartime industry. The result reflected great credit on the Assistant Director, A W Watson, and his constructor, A E Kimberley. Watson had designed the P boats of World War I.

Studies on two A/S designs began at the end of 1942 under A E Kimberley. One was basically an enlarged Flower with a single shaft and armed with a single Squid. The other was a twin-screw ship somewhat similar to the Rivers, with a twin Squid. The larger ship was preferred but, with the recognition that some smaller yards would not have slipways long enough to build the bigger ship, it was decided to build both designs. The Staff Requirements (that is, the official specification of requirements by the Naval Staff) were agreed and the design was frozen for two years from January 1943. The implications were a matter of concern; Goodall wrote,

This question brings us up hard at the onset against the difficulties attending anything like mass production of warships. The design must be fixed within the next month and by the end of the year [1942] no further changes can be accepted, though the ships will not commence to come out for many months and the last may not come out for more than two years from now.

The first ship, Loch Fada, was laid down on 8 June 1943 and completed on 29 March 1944.

The design received Board Approval on 7 May 1943, despite efforts by the First Lord, Alexander, who wanted to replace the twin Squid by another 4in gun – in an A/S ship! – Goodall was not amused. Initial armament was a single 4-inch, a four barrel pom-pom, two twin and two single Oerlikons; radar 277 (271 in a few early ships), asdic 144/147. Later increased with more 20mm and 40mm.

It was thought that at least 200 new escorts would be needed and first thoughts were for 120–45 of the twin-screw design (Lochs) and 70–80 single-screw ships (Castles). DNC’s production division under Hannaford then carried out a very careful analysis of the availability of slips of the lengths required. Matching slips and building times for individual yards, they came up with a definitive programme for 133 Lochs and 69 Castles. In December 1942, orders were placed for 226 sets of machinery. In total, 1,150 sets were completed during the war, many of the later ones being diverted to transport ferries (LST Mk 3).

In building this new fleet, it was intended to use structural engineering works, mainly bridge builders, to the maximum extent. They were to prefabricate hull sections of up to two and a half tons in weight, limited by shipyard cranes, which would be taken by rail to shipyards to be built into the ship, which imposed dimensional limits on the sections (29ft x 8ft 6in x 8ft 6in). The transverse frames were arranged with riveted boundary angles joined to flanged plate inner sections. The boundary angles were interrupted at plate edges and longitudinals. Longitudinals were flat plates welded direct to the shell. Beams and girders were all simple sections, angles, flats or flanged plates.

The sections used welding or riveting, according to the experience of the contractor. Riveting was usually employed for the assembly of sections in the shipyard. Careful inspection was necessary to ensure that sections made in different places actually fitted to make a fair ship. This worked well, ‘parts for prefabricated frigates coming together beautifully’.

It is interesting that contemporary documents refer to prefabrication as ‘on American methods’. Few of these firms had the capability for much plate-bending, lacking bending slabs or facilities for hot smithing, particularly double curvature, so much attention was paid to simplifying the shape. The hollow forward waterlines of the Rivers were made straight and the sheer of the deckline was formed by three straight lines. The stern lines were curved in one direction only. Model tests at Haslar showed that these changes in shape made little difference to the power required. The above-water form was built with flat panels to a considerable extent.

The structural design was led by J L Adam of the British Corporation Classification Society (now merged with Lloyd’s Register). He used longitudinal frames with deep transverse frames about five feet apart. Adam said in 1947 that the design was based on R Baker’s design for the much smaller minesweeper Seagull, the RN’s first all-welded ship. It was estimated that the cost was about 50 per cent greater than that of traditional structure, though there was a considerable reduction in building time. It was a very clever design for the day.

The first ship, Loch Fada, was built by John Brown, with the involvement of a special drawing office set up in Glasgow under the British Corporation and directed by the Warship Production Superintendent (Scotland). They converted the traditional shipbuilders’ drawings into a style that could be understood by structural engineers, quadrupling their number in the process. About half the fifty draughtsmen came from structural-engineering firms. The lines were laid off by the Henry Robb shipyard, who prepared many moulds (patterns). A very considerable number of firms were involved in this structural work. It was found that very light items such as partition bulkheads were too easily distorted in transit and were better built by the shipyard. There were some 100 subcontractors and about 1,360 units per ship.

Much of the equipment was ordered through a central office under ADNC(P) C J W Hopkins, RCNC. They supplied 500 tons of steel each week, complete offices for W/T, radar and asdic, pumps, rudders, watertight doors, valves, side scuttles, anchor and cable gear and other items too numerous to list here. The number of different types of valve was kept to a minimum and 2,000 were ordered each month. Pipe services, cable trays and ventilation trunking were designed and made by specialist firms. The schedule was geared to completing twelve ships per month. Careful scheduling was needed to ensure that the right bit arrived at the right time and place.

There were thirteen shipyards involved in building the Lochs, of which five acted as specialist outfitters. Six shipyards supplied complete bridges and superstructures. Shipyards of this era were very conservative in their practices and there were delays until opposition to prefabrication was overcome: ‘W Ayre doesn’t want bridge builders on the job – I got depressed, it looks as though the builders’ steady opposition to prefabrication is gaining ground.’ (4.1.43)

It was recognised from the start that these ships were far more complicated than earlier ships and that outfitting would be a problem: ‘Engines and boilers now the limiting factor in frigates assuming we get labour for fitting out.’ (20.3.43) In particular, it was estimated that 400 additional electrical fitters would be needed. None of these men were found and, indeed, more were lost to the army: ‘It is sticking out a mile that presently we shall have the ships ready to be fitted out but insufficient labour.’ (20.4.43) Two specialised outfit centres were set up, one at Dalmuir – ‘A bleak spot’ (6.4.43) – for Clyde-built ships and the other at Hendon Dock for the north-east coast. Machinery installation was by NE Marine Engineering and George Clark at Hendon Dock and by John Brown at Dalmuir. At first all went well: ‘Hendon Dock – work is going well. We must use this place more, it is well laid out and Hunter is a go-getter.’ (27.1.44)

By 1945, these centres were failing to keep up with the delivery of hulls, mainly because of shortages of skilled labour, and the docks were full of incomplete hulls awaiting fitting out. By this date, the battle was almost over and delay in completion was not serious.

Altogether, twenty-eight ships were completed as Lochs, nineteen became the Bay class AA frigates, two were coastal forces depot ships, two became despatch vessels (C-in-Cs’ yachts), four were converted to survey ships and fifty-four were cancelled. A few cost breakdowns are available and, although there was considerable scatter, the following is reasonably typical: hull £90,000; machinery £35,000; profit £7,000; other £3,000.

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