priorities are called CNO Priorities 1 and 2, and MCA Priority 3. Only CNO may authorize and direct Priority 1 and Priority 2 manning requirements. The MCAs may authorize and direct Priority 3 manning requirements only  for  their  assigned  activities. l Priority 1. Ships and activities whose mission success is deemed vital to the highest national interests and that require some degree of priority manning for an indefinite period of time may be authorized Priority 1 manning.  This  manning  category  is  limited  to  that portion  of  the  activity  absolutely  essential  to  mission success. . Priority 2. Ships and activities whose mission success is deemed essential to the national interests and that have specific need for increased manning for a specific period of time in order to carry out their mission may be authorized Priority 2 manning. This category of manning  is  limited  to  that  portion  of  the  activity absolutely essential to mission success. . Priority 3. Ships and activities that have a specific need  for  increased  manning  above  the  normal  manning level for mission accomplishment may be authorized Priority  3  manning  by  the  respective  MCA.  This category of manning is not normally authorized for periods  in  excess  of  1  year.  All  Priority  3  manning authorizations are automatically canceled on 31 March each year, unless a specific date has been previously authorized.  Requests  for  assignment  of  directed  priority manning are submitted according to the Manual of Navy Total  Force  Manpower  Policies  and  Procedures, OPNAVINST 1000..16G. TYPES OF DUTY Because  of  the  different  types  of  duty  stations throughout the Navy, the system is designed for the assignment of personnel among the various types of duty  classified  as  sea/shore  duty.  Each  of  these  types  of duty is credited as sea, shore, or neutral duty for rotation purposes. The types of duty are coded in Manpower, Personnel,   and   Training   Information   Systems (MAPTIS) and are reflected in each command’s EDVR as  a  sea/shore  code  (SSC).  Type  duty  codes  are  as follows: l Shore duty (SSC 1) is duty performed in CONUS (the 48 contiguous states) land-based activities and long-term  schooling  programs.  (Long  term  is  defined  as 18 or more months; school assignments of less than 18 months are considered neutral duty.) .  Sea  duty  (SSC  2)  is  duty  performed  in commissioned  vessels  or  activities  in  an  active  status home-ported  home-based  in  CONUS  that  operate  away from their home port/home base in excess of 150 days per year. • Overseas  shore  duty  (SSC  3)  is  duty  performed in overseas land activities that is credited as sea duty for rotational  purposes  as  determined  by  BUPERS. . Nonrotated sea duty (SSC 4) is duty performed in commissioned vessels in an active status home-ported overseas  (outside  the  48  contiguous  states)  or  in activities that operate away from their overseas home port/home base in excess of 150 days per year. . Neutral duty (SSC 5) is duty in activities that would normally be designated as shore duty for rotation, but where the members assigned are required to be absent 100 to 150 days per year from the corporate limits of their duty station while accomplishing their assigned tasks. School assignments of less than 18 months are included  in  this  category. . Preferred overseas shore duty (SSC 6) is duty performed  in  overseas  land-based  activities  that  is credited  as  shore  duty  for  rotational  purposes  as determined by BUPERS. . Partial sea duty (SSC 7) is duty performed in overseas land-based activities that is credited as shore duty  for  rotational  purposes,  but  where  members assigned receive partial sea duty credit according to guidelines  established  in  the  ENLTRANSMAN, chapter 4. l Double sea duty (SSC 8) is duty performed in commissioned  vessels  or  activities  in  an  active  status that  operate  away  from  their  home  porthome  base  in excess of 150 days a year, but where due to the nature of their mission are awarded double sea credit for the tour  served. Rotation among sea, shore, and overseas activities is  directly  influenced  by  the  number  of  personnel available   for   assignment,   billets   authorized,   the qualifications of the individual, time-on-station (TOS), and permanent change of station (PCS) finding. The primary consideration in assignment of personnel to a billet is that the member possesses the required skills necessary to fill that billet. Also of prime consideration in rotation plans and policies is the conservation of PCS funds. The type of duty to which an individual will be reassigned upon completion of a tour is dependent upon 3-3