1:600 "A" class submarine. Very modern for their day, features of note are the raised RDF scanner, retracted bow planes, forward external torpedoes in streamlined bow, and casing aft over the external tubes. A 4" gun was caried througout their lives, although the 20mm cannon was removed post-war. © Andrew Arthur

This class was an improved "T" class, and because it was seen as a 'fresh start' for RN submarines, the name letters"W", "Y" and "Z" were skipped, and "A" selected.
With the end of the European war in sight, the Japanese & Far East theatres were seen as the most likely area of operations, and as such, a good range, fast surface speed and good endurance were necessary. At the same time it was decided to introduce new technical advances, the most important being the all-welded hull, the snorkel, air conditioning & good streamlining.
Until the "A" class, the Royal Navy had not considered the 'snorkel' worth introducing and slowing production, training etc. ( although it had by now been used for some time by the Germans ). British submarines never really faced stiff competition from an advanced enemy escort force, and had the relative luxury of being able to surface at night 90% of the time to re-plenish air and re-charge batteries. Also, unlike many other countries' submarines, a lot of attention and space was paid to air scrubbers, coolers and re-circulators to keep a submarine's air bearable for many long hours.
The result was one of the best designed of all diesel submarine of their period and long after. They had good sea performance, good armament and a greatly reduced underwater noise level. Also, for the first time ever, a special air conditioning system was installed, all air being sucked into an air conditioning unit from throughout the ship, cooled & reduced in humidity and CO₂ and if necessary, extra O₂ could be bled in, to keep the submarine's atmosphere, cool, dry and fresh.
Unfortunately, this class were not completed in time for the boats to take part in WWII , but they served for many years and were effectively the backbone of the submarine service until the introduction of the Porpoise and Oberon classes of submarine : and the "A" class were later modified to have a very similar appearance & performance with the Porpoise and Oberon classes.
The last of the "A" class in service was HMS Andrew who was paid off in 1974.