Military documents use a 24 hour clock, with noon being 1200 hours and midnight being 2400   hours.  The day of the month precedes the time and the month follows.  For example 051200 July would be 12 noon, on July 5.  Unless otherwise specified, all times are local.

An Army is designated by an Arabic numeral and consisted of two or more Corps.

A Corps is designated by Roman Numerals (X designated 10th Corps) and consisted of two or more divisions.

An Infantry Division consisted of three regiments, an armored battalion, four artillery battalions, a combat engineer battalion and numerous support units, such as medical, quartermaster, military police, graves registration, etc.  They were referred to as "Triangular".  The First Cavalry Division, in spite of its name, operated as infantry during World War II in the Pacific.  It had two brigades, each with a headquarters troop (company) and two squadrons (regiments) each with a headquarters troop.  Each regiment had two squadrons (battalion), each with a headquarters troop.  In March/April 1949 the First Cavalry Division was redesignated First Cavalry Division (Infantry) with the same structure as other infantry divisions with companies replacing troops and battalions replacing squadrons. 

An infantry regiment consisted of three battalions and a regimental headquarters company.

An infantry battalion consisted of three rifle companies, a heavy weapons company and a battalion headquarters company.

An artillery battalion consisted of three firing batteries of six guns each, a headquarters company and a service company.

An infantry company consisted of three rifle platoons, a heavy weapons platoon and  a company headquarters platoon.

A 1950's era rifle platoon consisted of a platoon leader and four twelve man squads.  It had a strength of about 49 men.  Sometime in the 1950's the twelve man squads were reduced to nine man squads for a strength of about 37.

Twelve man squads were made up of a squad leader, a Browning Automatic Rifleman (BAR), an assistant BAR and nine riflemen.  With the change to nine man squads, the number of riflemen was reduced to six.  Marine Corps squads had much more firepower as they contained between three and four BAR's.

RCT means Regimental Combat Team, which consists of three battalions plus armor, artillery and other units as assigned by division.

BCT means Battalion Combat Team, which consists of the battalion plus armor, artillery and any other units assigned by division or regiment.

ROK stands for Republic of Korea.

NKPA stands for North Korean Peoples Army.

CCF stands for Communist Chinese Forces.

G-1 stands for Personnel at division or higher level.  S-1 is the designation used at lower units.

G-2 stands for Intelligence at division or higher while S-2 is used at lower level units.

G-3 stands for Operations at division or higher and S-3 is used at lower level units.

G-4 stands for Supply and Logistics at Division and higher units while S-4 is used at lower levels.

MSR stands for Main Supply Route.

MLR stands for Main Line of Resistance.

I&R stands for Intelligence and Reconnaissance.

AW stands for Automatic Weapons (sub-machine guns and machine guns).

AAA stands for Anti-Aircraft Artillery.  In the war in Korea where we had air superiority almost everywhere, they were used as anti-personnel weapons and were very effective against massed attacks by North Koreans and Chinese forces.

SP stands for Self-Propelled (Artillery).

KIA stands for Killed in Action.

WIA stands for Wounded in Action.

MIA stands for Missing in Action.

SWA stands for Seriously Wounded in Action.

IPW stands for Interrogation, Prisoner of War.

FA is an often used abbreviation for Field Artillery.

Bn is a common abbreviation for Battalion.

WP stands for White Phosphorus (artillery, mortar and hand grenades).  They were used to set fire to grass, bushes, trees, buildings, etc.  White phosphorus also inflicted pretty nasty burns on people.

VT stands for Variably Timed.  Used in artillery shells which had fuzes designed to detonate the shell at a designated height in the air above the target.  They were especially effective against troops in the open unarmored vehicles.

BAR stands for Browning Automatic Rifle.  It was equipped with a 20 round magazine using standard 30 caliber rifle ammunition.  It could fire either semi-automatically (only one round with each pull on the trigger) or automatically (with the trigger pulled and held, it would fire continuously until the magazine was empty)  It usually had a bipod attached toward the end of the barrel.

CIC stands for Counter-Intelligence Corps.  Members were often multi-lingual and they interrogated prisoners, checked our installations to see if they were secure against enemy intruders.  They also acted as liaison with local police.  During the Korean War, they worked with South Korean police.  In Occupied Japan, they worked with Japanese police.

MOS stands for Military Occupational Specialty.  Every person in the military has a MOS as a primary and some have one or more secondary specialties.  It compares with a job description in civilian life.

TO&E stands for Table of Organization and Equipment.  Every military unit has one.  They specify the number, rank and MOS of all personnel authorized in any unit.  It also specifies the number and type of any equipment such as vehicles, weapons, radios, etc which are authorized in a unit.  The numbers change depending on whether it is a peacetime unit (as were all of the units who went from Japan to South Korea) or whether it is for wartime (a status which all units which went to Korea eventually  attained.).