US Army boat units certainly served in WWII. And the US Army's 9th Infantry Division conducted riverine operations in MR-4 (Military Region 4/Mekong Delta) South Vietnam. However, the US Navy operated it's Brown Water Navy's Riverine Forces, not the US Army.
The USN Brown Water Navy consisted of several riverine units, just to name a few of them: Riverine Assault Squadrons; Riverine Patrol Squadrons; Coastal Squadrons; River Support Squadrons; Mobile Riverine Forces; etc.
And, they were organized differently, for example, a "Riverine Assault Squadron" might have (numbers will always vary based upon losses or deadlines (deadline=down for maintenance): 2 divisions; each div=8 ASPB/3 Monitors/13 ATC/2 CCB (ASPB-Assault Support Patrol Boat (aka Alpha Boat); ATC-Armored Troop Carrier; CCB-Command & Control Boat; a Monitor was a river battleship).
A PBR (Patrol Boat River) squadron might have 5 riverine divisions; each division consisting of 4 or 5 sections (each section consisting of 10 Pibbers (PBRs). (Nick-named the "Plastics", all fiberglass 32 footers).
PCF (Patrol Craft Fast/SWIFT BOATS) were assigned to "Coastal Squadrons": A squadron might have 5 divisions; each division consisting of up to 19 Swift Boats. (All aluminum 50 footers, twin diesel engines, 1 officer & 5 crewmen; 3 .50 Caliber Browning Machineguns, and one 81mm mortar).
Life aboard those riverine boats was patrolling by day, and if intelligence indicated strong enemy activity, patrols were conducted at night. Sailors stayed in shore or floating barracks; or aboard their crafts, if the campaign called for it.
During the Vietnam War, a US Army "Troop" was a US Cavalry "Company." Example(s): "A" Troop, "B" Troop, "C" Troop, etc. The Australian Army in Vietnam called their "Companies" a "Squadron", and called their "Platoons" a "Troop." (During the war) The US Army standard "Infantry" Platoon was approximately forty men. An "Armor" platoon (in Vietnam) consisted of 5 Patton tanks per platoon; with 20 tank crewmen per platoon...led by a 2nd or 1st Lieutenant.
There is no Army National Guard basic training. It is basic training at one of the US Army's active duty training base. All active, reserve, and guard members train together as one. The platoon guide is basically a leader of the platoon.
A platoon (in the US Army) is the smallest military unit led by an officer. Two or more platoons make a company; a company is commanded by a captain.
Depending on what type of platoon, it could be 25 - 40.
US ARMY Army Group Army Corps Division Regiment Battalion Company Platoon Squad
platoon leader Lt. William Calley
Someone who's job it is to make sure that the lifeboats on a ship are all safe and stocked with necessary supplies.
The life blood of a US Army company is the squad leader, regardless of rank. The typical rank for a squad leader is Staff Sergeant (E-6). The squad leader is responsible for the training and care of all soldiers in the squad. While the platoon sergeant, first sergeant, platoon leader, and company commander all play important roles, the person who is responsible to ensure the work gets done is the squad leader.
The life blood of a US Army company is the squad leader, regardless of rank. The typical rank for a squad leader is Staff Sergeant (E-6). The squad leader is responsible for the training and care of all soldiers in the squad. While the platoon sergeant, first sergeant, platoon leader, and company commander all play important roles, the person who is responsible to ensure the work gets done is the squad leader.
The Field Manual FM 3-21.8 Infantry Rifle Platoon and Squad replaced FM 7-8.
In the US Army, US Marine Corps, US Air Force, there are two types of LIEUTENANTS: 1. 2nd Lieutenant-Gold Bar, and a newly commissioned officer. Normally leads a platoon in the infantry, or a tank platoon of an Armor Battalion. During the 20th Century and ending with the Vietnam War, a US Tank Platoon consisted of 5 tanks, and a US Infantry Platoon consisted of approximately 40 Infantrymen. THIS HAS CHANGED AFTER VIETNAM and into the 21st Century. 2. 1st Lieutenant-Silver Bar, and now an experienced officer. Normally designated the XO (Executive Officer of a Company); For the 20th Century ending with the Vietnam War: A US Army Infantry Battalion consisted of approximately 4 to 5 companies (3 or 4 line companies A, B, C, or D, and a Headquarters Company, HHC). Each Company was Commanded by a Captain. The XO was second in command of the Company. A US Army Armor Battalion (Tank Battalion) consisted of approximately 3 to 4 companies, same as with the infantry. Each tank company consisted of 3 tank platoons and 1 Headquarters Platoon (1st, 2nd, 3rd tank platoon consisting of 5 tanks each, and headquarters platoon had 2 tanks); total 17 tanks per company. 2nd Lieutenants led their 5 tank platoons, and the 1st LT was the XO of the tank company, with a Captain as the Company Commander. Again, this all ended AFTER the Vietnam War. The US Army REORGANIZED after the Vietnam War. The US Navy and US Coast Guard: A Lieutenant is EQUAL TO A CAPTAIN in the Army, Marines, and Air Force. The insignia for a Navy Lieutenant (two bars attached together) is a captains rank. A US Navy/US Coast Guard Captain insignia rank is the EAGLE; in the Army, Marines, and Air Force an EAGLE is a full bird COLONEL. So, a US Navy Captain is equal to a US Army, Marine, Air Force Colonel.
For the sake of producing a high volume of casualties on the battlefield. Even today, they serve the same function - in a US Army light infantry platoon, for example, the two medium/general purpose machine guns account for 70% of that platoon's overall firepower.