NOTE ON FIRST LINE STRENGTH
 
      
 
 
As the term "first line strength" is employed in 
      different senses by different authorities it is necessary to 
      define the sense in which the phrase is employed in the foregoing 
      memorandum and elsewhere in Air Ministry announcements.
 
      
 
 
The aircraft provided for a Royal Air Force squadron fall 
      into four categories:- (1) the Initial Equipment aircraft, (2) 
      the Immediate Reserve, (3) the Workshop Reserve, and (4) the 
      Stored Reserve. 0nly "Initial Equipment" aircraft are 
      operated, and the various categories of reserves are maintained 
      to ensure that the "Initial Equipment," is kept up 
      to establishment in peace and war. Thus the "Immediate Reserve" 
      represents a reserve of aircraft kept with a squadron to make 
      good loss by crashes, etc; the "Workshop Reserve", 
      as the name implies, that margin of aircraft which experience 
      shows will normally be under repair at any one time. Finally, 
      the "Stored Reserve" is the provision made to meet 
      war wastage until such time as it is covered by war production.
 
      
 
 
The "Initial Equipment" of a squadron is thus its 
      "first line"; and all other aircraft which are provided 
      for the squadron, though identical in type with the initial equipment 
      aircraft, have no other function than to preserve the first line 
      intact against wastage. The first line strength of a squadron 
      is thus the number of initial equipment aircraft it possesses 
      - a number standardized for each type of squadron. The first 
      line strength of the whole Air Force is the aggregate of the 
      initial equipment of all operational squadrons. The first line 
      strength thus excludes reserves of all categories and training 
      aircraft of all categories.