Officers
take command in their respective services in accordance with their
dates of rank in the line, the senior, unless otherwise ordered,
taking command, whether regular or reserve. The command of a task
force or group composed of commands from two or more services devolves
upon the senior commanding officer present in the force or group
unless otherwise designated by the appropriate common senior, acting
for the President.

The obvious exceptions to this are that officers outside the line
(that is, commissioned in specialized branches or corps) cannot
command line organizations. They may, however, in the Army and Air
Force, command organizations within the structure of their own corps.
Non-rated officers in the Air Force and Navy are not eligible to
command tactical flying units. As a specialized case of command, the
assigned first pilot and airplane commander of any aircraft continues
in command even though a pilot senior in rank may be aboard.

Retired officers of the Army rank at the foot of active officers of
the same grade; those of the Navy according to date of rank.

Changing personnel policies have been reflected by frequent revisions
of the scale and grade given noncommissioned leadership. This subject
should therefore be checked against current regulations. But as a
rough guide, the following can be taken as the corresponding
noncommissioned grades and rates in the services:

-----+------------------+-------------+-------------+-------------
PAY | NAVY AND | ARMY | AIR | MARINE
GRADE| COAST GUARD | | FORCE | CORPS
-----+------------------+-------------+-------------+-------------
E-7 |Chief Petty |Master |Master |Master
|Officer |Sergeant |Sergeant |Sergeant
-----+------------------+-------------+-------------+-------------
E-6 |Petty Officer |Sergeant |Technical |Technical
|First Class |First Class |Sergeant |Sergeant
-----+------------------+-------------+-------------+-------------
E-5 |Petty Officer |Sergeant |Staff |Staff
|Second Class | |Sergeant |Sergeant
-----+------------------+-------------+-------------+-------------
E-4 |Petty Officer |Corporal |Sergeant |Sergeant
|Third Class | | |
-----+------------------+---------