the Japanese meant that more should be ordered, but in the meantime initial development work shifted to the concept of the Trade Protection carrier, or light carrier as it came to be known.
There were of course issues with the allowed displacement under the London Naval trea ty. This allowed the RN 135,000 tons of carriers. The existing carriers could be discarded at any time (they were deemed to be experimental), but they still couldn't build all they wanted to. This was a continuing problem due to the global commitments of the navy. The current design was hoped to come in at around 24,000 tons. Building 5 of these would allow one additional, smaller carrier in the range 12,000 tons - 15 ,000 tons, or building 4 would allow 3 smaller carriers (once the existing ones had been scrapped). The current proposal was for a minimum of 4 fleet carriers; this allowed one to be deployed in each main area (Home, Med and the Far East), while allowing for one to be unavailable due to maintenance and refit. If a fifth fleet was built, this allowed a second to be sent to whichever area was under the most threat. The final smaller carrier would normally be used for training, but it would also be available either for deployment or to relieve a fleet carrier in a lower threat area. It was hoped that something more suitable could be arranged when the talks came up for renewal.
The idea of a smaller carrier for use on the trade routes and to cover commerce raiders had been considered for many years, but with not enough aircraft coming from the RAF to fill the existing carriers, it had always fallen victim to ships considered to be needed more urgently . There wasn't, after all, much point to a trade protection carrier without planes.
Such a vessel would be ideal for supporting a hunting group looking for a commerce raider, as its aircraft could cover a far greater area than the cruisers usually assigned to that task. It would also be an ideal support for high value convoys in dangerous waters, and suited to task force support which did not merit the use of a fleet carrier. It was intended such a ship would be of similar cost to a cruiser, and as such could be risked in areas when a fleet carrier would be considered too valuable.
Given that the displacement of the fleet carrier was around 25,000 tons, the first studies of the CVL were around half this. As the vessel was expected to be used and risked as a cruiser, it was important that cost be kept to a minimum, and corners could be cut in a way that wasn't considered sensible for the fleet carrier. The capacity was to be around 25 planes. A number of studies and proposals were investigated, and these slowly consolidated around a proposed ship.
This would displace about 12,500 tons, and carry 25 aircraft, with space allowed for reasonable maintenance work (as hunting groups in particular were often away from base support for long periods). This would fit in with the displacement limits, and some hope was entertained that small carriers in the 10,000 - 12,000 ton range might be exclude in future (as they had been until the London treaty in 1930), in which case this ship would serve as a model for a slightly smaller ship. Considerable agonising had been done of the fitting of a TDS, as it was felt that the usage of such a ship was such that a torpedo from a submarine would be one of the most likely threats. However it was extremely difficult to fit a useful TDS into such a small vessel. A solution was proposed that basically solved the problem by going around it; instead of a TDS, the ship would be well subdivided, and drums would be installed into spaces to provide buoyancy in case of underwater damage. Such a system was planned to be fitted to liners marked down as auxiliary cruisers. To aid the ships survival, the engine and boiler rooms would be split so one torpedo wouldn't take out both.
In order to keep the displacement down, as well as the cost, it was decided that the ship would only