The locomotive also carried a similar "air-smoothed" casing to the Merchant Navy class. This was not regarded as streamlining by Bulleid, a fact demonstrated by the flat front end. Authorities differ as to the purpose of the casing. According to Creer it was intended to be an aid in cleaning the locomotive with carriage washers to reduce labour requirements during the post-war period, whereas Bradley asserts that the intention was to lift the steam and exhaust gases away from the cab. As with the Merchant Navies, the class soon gained the nickname "Spam Cans", due to the resemblance to the distinctive tin cans in which "SPAM" was sold.