There were basically two Airfields on Ceylon, namely Ratmalana and China Bay (called Trincomalee by the Royal Navy, after the nearby port and harbour). The sudden build up of British aircraft strength lead to the construction of two satellite airfields, one at a racecourse outside Ratmalana, and the other at Katukurunda inland from China Bay.
Ratmalana. 4 x heavy AA guns, 12 x light.
Squadrons - No 11 (16 Blenheims); No 30 (24 Hurricanes); No 258 (16 Hurricanes); and No 803 (12 Fulmars).
Racecourse.
Squadron - No 806 (12 Fulmars).
China Bay/Trincomalee. 20 x heavy AA guns, 31 x light.
Squadrons - No 261 (19 Hurricanes); No 273 (6 Fulmars); and No 788 (6 Swordfish). There was also a composite squadron, not numbered, acting as a replacement pool. It was equipped with an assortment of about 20 Hudsons, Albatrosses, Fulmers, Albacores and Swordfish. A large proportion of them seem to have been unserviceable for most of the time.
Katukurunda.
Squadron - No 814 (from Hermes).
Koggala Anchorage.
Squadron - No 413 (7 Catalinas).
Carrier Aircraft.
Indomitable - No 800 (12 Fulmars); No 827 (12 Albacores); No 831 (12 Albacores); and No 881 (9 Sea Hurricanes).
Formidable - No 818 (9 Albacores); No 820 (12 Albacores); and No 888 (12 Martlets).
Hermes - No 814 (9 Swordfish).
By the time of the Japanese attack this squadron had been disembarked and the aircraft deployed to either China Bay or Katukurunda. When Hermes undertook her last voyage she had no aircraft on board.
Bibliography.
"Encyclopaedia Britannica", various editions.
"Ships of the Royal Navy, Vol 1 & 2", by J J Colledge. Published by Daniel & Charles: Newton Abbot, 1969.
"Battle Summary 15, Naval Operations off Ceylon 29th March to 10th April, 1942", HMSO, 1943.
"Carriers at War", Strategic Studies Group Pty Limited, Drummoyne, Australia.
The Japanese Sweep Into the Indian Ocean Page 3