Sloops were to be designed primarily
      for minesweeping and simply fitted for their survey role.  
          
          The fit for surveying was similar to
      the Convoy Sloops. No armament was to be fitted, though the Survey
      Minesweeping Sloops were fitted for but not with the standard Halcyon
      armament of 2 x 4-inch guns and small arms. A large chartroom was built at
      the after end of the forecastle deck, and the bridge was enlarged to make
      it more commodious for sextant angle fixing. A large derrick was fitted on
      the forecastle for handling survey beacons (floating marks like very large
      dan buoys).  
          The two types could be distinguished
      at a glance by their masting. FRANKLIN and SCOTT
      the surveying ships, stepped their foremasts on the forecastle, rigging
      the beaconing derrick directly to the mast. 
          
          
          
          FRANKLIN 1947 
          
          SCOTT
          GLEANER
      and JASON, the minesweeper conversions,
      though built in the surveying configuration, stepped their foremasts in
      the standard Halcyon position aft of the
      bridge, and carried a stump for the derrick in the W gun position. All, in
      their pre-war surveying configuration, carried pole mainmasts stepped just
      forward of the chartroom.  
      
          
        
          GLEANER 1937  
    
          
          
          
          JASON 1938
          
          The four
      ships were built as follows:
        
          
            
              | 
              
              Ship
               | 
              
              
              Built
            by  | 
              
              
              Laid
            down  | 
              
              
              Launched
               | 
              
               
              
              Completed
                | 
            
            
              | 
              
              GLEANER
               | 
              
              Gray,
              
              Hartlepool
              
              
               | 
              
              
              
              
              
              17.06.1936
            
               | 
              
              
              
              10.06.1937
               | 
              
               
              
              
              30.03.1938
                | 
            
            
              | 
              
              JASON
               | 
              
              Ailsa,
            Troon  | 
              
              
              
              
              12.12.1936
            
               | 
              
              
              6.10.1937 | 
              
               
              
              21.04.1938 
                | 
            
            
              | 
              
              
              FRANKLIN 
               | 
              
              Ailsa,
            Troon  | 
              
              
              
              
              17.12.1936
            
               | 
              
              
              22.12.1937 | 
              
               
              
              14.06.1938 
                | 
            
            
              | 
              
              SCOTT
               | 
              
              
              
              
              Caledon 
              , 
              Dundee
              
              
               | 
              
              
              
              
              30.08.1937
            
               | 
              
              
              23.08.1938 | 
              
               
              
              14.10.1938 
                | 
            
          
          
          
          GLEANER,
          JASON 
          and 
      FRANKLIN
      all started surveying in home waters in the summer and autumn of 1938, to
      be joined by SCOTT in 1939. FRANKLIN
      was the only one to serve overseas, working on the Labrador coast
      in the summer of 1939.  
          JASON and
          GLEANER quickly reverted to general service on the outbreak of war.
      They were armed, and became to all intents and purposes standard Halcyons,
      and like their sisters were employed as much on escort duties as on
      minesweeping. FRANKLIN and SCOTT
      each received a single 3-inch AA gun in a bandstand for'ard of the
      foremast on the forecastle and a varied fit of small arms. They kept the
      big chartroorn aft, but lost their mainmasts to topweight compensation.
      They were employed on a variety of tasks, mainly in support of minelaying
      and mine clearance, but also surveying new fleet anchorages and bases in
      the United Kingdom and northern waters. One little-known exploit was that
      when BISMARCK broke out SCOTT was send ahead of HOOD and PRINCE
      OF WALES to check on the position of the edge of the pack ice off
      Greenland. Fortunately for her she did not encounter the German squadron. 
          
          
          After
      the war FRANKLIN and SCOTT
      were quickly disarmed and restored to full surveying status. A minor
      distinction which identifies them post-war is that while FRANKLIN'S
      mainmast was restored to its pre-war position for'ard of the chartroom, 
          SCOTT'S
      was stepped on the chartroom roof. For a period in 1946-47, while
      operating in the Thames with HDMLs attached to her, FRANKLIN
      had a heavy rubbing strake fitted on her quarters just above the
      waterline. Though SCOTT also operated with
      MLs at this time she was not, apparently, fitted with this. 
          
          Though both JASON
      and GLEANER survived the war, neither
      returned to surveying. Instead, SEAGULL and SHARPSHOOTER
      were given to Hydrographer in 1945 and converted to replace them.
      They introduced the third variant in surveying
      Halcyon masting, since though they, like their predecessors, were
      fitted with a beaconing derrick and stump on the forecastle and maintained
      their foremast aft of the bridge, they did not have their mainmasts
      restored, so a Halcyon in surveying white and
      buff without a mainmast must be one of these later two. 
       
      
          
          
 
          SHARPSHOOTER 1950 Chartroom added postwar
          
            
              SEAGULL  
              
            
          
          SHARPSHOOTER
      went out to the Far East in 1946 to relieve the verminous converted yacht WHITE
      BEAR, and surveyed round the Malay
      Peninsula and Borneo for two years before the arrival of the first of the
      converted BAYS - HMS DAMPIER. Apart from this,
      all four spent the remainder of their days in home waters. 
          
          SEAGULL was
      the first to go. Having spent the 1950 season with a reduced crew mainly
      in Torbay, she paid off that autumn, and was scrapped by Demmelweek and
      Redding in Plymouth in 1956. FRANKLIN was
      paid off at the end of the 1952 season and went to the breakers at Dunston,
      also in 1956.  
          
          
  
          
          HMS 
          SHACKLETON 
          SHARPSHOOTER
      was renamed SHACKLETON in June 1953 to bring
      her into line with all the other surveying ships named after famous
      explorers and surveyors. At this time she was fitted with a topmast to her
      derrick stump to carry a forward steaming light, needed after the
      exemption of warships from the Collision Regulations for lights was
      written out in their 1952 revision. She soldiered on until 1962, when she
      ended her surveying season and entered Devonport with the Hydrographer
      embarked on 9th November to pay off for disposal. She was broken up at Troon
      at the end of 1965. SCOTT lasted two more
      years in service, paying off in November 1964 but preceding her sister to
      the breakers in Troon, arriving in June 1966.
          
          