At least for shipping, the processes by which ships were produced were actually more chaotic and less under government control in WWI, rather than WWII. If the numbers of ships produced dropped in WW this was likely more attributable to the practical collapse of the British shipbuilding industry in the 1920s and 1930s than to any change in policy during either war.

Throughout the period in question, the main mechanism by which warships were produced changed little. The naval staff set a requirement for a new design, which was passed to the Royal Corps of Naval Constructors (RCNC). This was a civil service body which provided the Admiralty with naval architects. The RCNC would draw up draft designs, and pass them back to the naval staff for comments. This process of refinement (which I am simplifying here) would continue until the naval staff selected the draft it preferred. The RCNC would then draw up a detailed design for the ship. Once the design work was finished, the Admiralty solicited tenders from shipyards. These were mainly private concerns; the Royal Dockyards at Plymouth, Portsmouth and Chatham had much less space for building than the private shipyards. The most attractive offers were chosen, though orders were usually spread out between yards to ensure that the industry stayed competitive. The ship's machinery, armour and armament might be ordered from the same company, or be bought from another contractor. The Admiralty and RCNC would maintain a strict level of scrutiny over the build until it was complete.

For merchant shipbuilding, though, it was a very different story. In peacetime, the main drivers were the shipping companies. They ordered their own designs from the shipyards, or bought off-the-shelf designs from them, albeit with oversight from the Board of Trade. This state of affairs continued into WWI, but by 1916, proved to be poorly suited to the demands of a modern war. In December 1916, a new office, that of Shipping Controller, was formed. He immediately began a major emergency shipbuilding programme, using standardised designs. This, however, ran into shortages - of labour, of steel and of shipyard space. The Army had recruited or conscripted many men from the shipbuilding communities of the North of England and Scotland; this included the skilled labour that Britain's shipyards had relied upon. While the RN had been able to secure exemptions and prohibitions to protect the shipbuilding industry, there were few reserves of men to expand it. Steel was in high demand for every part of the war effort, but the men and materials to produce it were in short supply. The Admiralty had monopolised much of Britain's shipbuilding capacity. This included yards that had traditionally built merchant ships, as new escorts were designed to suit such yards. To solve these problems, the Shipping Controller was brought into the Admiralty, with the Third Sea Lord (responsible for naval shipbuilding) being given the role. A new Third Sea Lord, Sir Eric Geddes, was also appointed. He was a civilian in a traditionally military role, but had also been instrumental in sorting out the logistical mess in France earlier in the war. Under Geddes, the shipbuilding programme was intensified. He set an annual goal for shipbuilding of 4.6 million tons, with 3.1 million of these being merchant shipping. However, he would fall short on these goals. Production in 1917 was just 1.2 million tons, while 1918 it was even lower, at 0.76 million. This was largely due to labour issues; too many men were working on naval shipbuilding or on repairing and refitting ships.

In WWII, things were very different. The British government had learned from the mistakes of WWI, and had no desire to repeat them. In the run-up to war, shipyards were assessed for their ability to mass-produce merchant ships. In October 1939, when it became clear that the Germans would continue their strategy of unrestricted submarine warfare, a Ministry of Shipping was formed. This would oversee the building and operations of Britain's merchant ships. In February 1940, responsibility for construction was transferred to the Admiralty, which would retain this until the end of the war. Initially, the shipbuilding programme relied on churning out standardised sets of machinery; individual yards could then fit these machinery sets into hulls that they were experienced with building. Over time, though, the programme moved more towards centralised designs. These 'Empire' ships were, essentially, the British version of the American 'Liberty' ship (with both ships being built to similar designs). The ships were either built directly by the Admiralty, in which case the ship would be owned by the Ministry of Shipping who licensed it out to a shipping line to operate, or the Admiralty would grant a licence to a shipyard to produce a ship for a private owner. This allowed for much greater efficiency in construction and operation. However, the programme did run into many of the problems that had popped up in 1917, as well as new ones. Steel was again in short supply, for similar reasons. Bombing disrupted yards and displaced workers - the major shipbuilding centre of Clydebank was heavily bombed in 1941, which destroyed much of the town. Many of the other problems, though, were caused by the poor state of the shipbuilding industry in the 1920s and 1930s.

Immediately following WWI, the British government made swingeing cuts to naval expenditure, in order to pay down war debts and refocus the economy towards peacetime production. This was driven by both Geddes (as chair of the Committee on National Expenditure) and by Churchill (as Chancellor). At first, this had little effect on the shipbuilding companies, who could still make money producing merchant ships to replace the losses of WWI. However, it put the armaments companies, who produced weapons and armour for warships, on a shaky footing - the Coventry Ordnance Works, one of the major companies that produced naval guns, lost its major backers in 1919, but struggled on to 1925. The prospect of building four new capital ships of the 'G3' class helped to prop up the industry, but in 1921, the Washington Naval Treaty put an end to this. The shipbuilders also found themselves running into issues. There was less demand for new merchant tonnage than expected - mass produced ships from America's emergency shipbuilding programme and German ships seized as reparations both flooded the market. In 1925, the Bank of England stepped in, and began to restructure the armaments industry. The two main armaments companies, Vickers and Armstrong Whitworth, were combined into one organisation, following the near bankruptcy of Armstrongs. Shipbuilding steel was similarly consolidated into a few major companies - Firth-Brown, Beardmore and the English Steel Corporation.

The shipbuilding industry managed to hang on on the few small naval and merchant orders until the Great Depression. This nearly completely destroyed the market for new merchant ships. With no new orders, shipyards could not make money. By 1932, unemployment in the shipbuilding industry was at ~60%. The government was unwilling to spend money to stimulate the industry, so to solve the problems and ease competition for the few orders that were left, in 1930, the major shipbuilding firms and the Bank of England formed National Shipbuilders Security Ltd (NSS). NSS aimed to cut down the excess capacity in the shipbuilding industry by buying up struggling yards and selling off their equipment and land for non-shipbuilding uses. This happened to yards large and small, with the two most famous being Beardmore's yard on the Clyde (the largest on the river) and Palmer's in Jarrow. While this allowed the rest of the industry to survive, it had three significant negative effects. Firstly, it destroyed the physical infrastructure of shipbuilding. In 1930, Britain had some 459 large slipways over 250 ft in length. By 1939, this had dropped to 266, putting a lower cap on the number of ships that could be built simultaneously. Secondly, it destroyed the labour supply for shipbuilding. With unemployment so high and the industry in such an uncertain state, the skilled workforce that shipyards relied upon disintegrated. Many emigrated or moved to the industrial centres of the Midlands to find alternative employment in more stable industries. Few apprentices wanted to join the industry, so there was little ability to expand it in a hurry. Finally, there was no capital available for investment into new technologies and facilities. This meant that Britain's shipyards in 1939 looked very similar to how they looked in 1914. In particular, the lack of welding equipment was a major problem. Welding was a much less skilled job than riveting, making it much easier to expand the workforce - this is how the American yards of WWII managed to achieve such high rates of production, using a vast workforce equipped with welding torches. All of this meant that Britain's shipbuilding industry was much less prepared for a vast building programme than it had been in 1914.