What is a Field Manual?

TRADOC Regulation 25-36

"A field manual is a Department of the Army publication that contains principles, tactics, procedures, and other doctrinal information. It describes how the Army and its organizations conduct operations and train for those operations. FMs describe how the Army executes operations described in the ADPs. They fully integrate and comply with the fundamental principles in the ADPs and the tactics and principles discussed in the ADRPs."  [Emphasis added.]

To say that, under Doctrine 2015, a field manual describes "what" and an Army Techniques Publication describes "how" is to put an entirely artificial construction upon doctrine.  It is also inconsistent with the regulation that governs doctrine.

Some helpful definitions.

Operations. (1) a series of tactical actions with a common purpose or unifying theme. (JP 1); some examples … unified land operations; theater army operations; corps and division operations; offensive and defensive operations; stability operations; cyberspace operations; etc.  (2) military action … strategic, operational, tactical, service, training, or administrative military mission. (JP 3-0); some examples of operations … Operation Overlord; Operation Linebacker; Operation Urgent Fury; Operation Just Cause; Operations Desert Shield and Desert Storm; Operations Enduring Freedom and Iraqi Freedom.

Tactics are the employment and ordered arrangement of forces in relation to each other (JP 1-02). It includes the ordered arrangement and maneuver of units in relation to each other, the terrain, and the enemy in order to translate potential combat power into victorious battles and engagements. Effective tactics translate combat power into decisive results. Tactics vary with terrain and other circumstances; they change frequently as the enemy reacts and friendly forces explore new approaches. Applying tactics usually entails acting under time constraints with incomplete information. Tactics always require judgment in application; they are always descriptive, not prescriptive. In a general sense, tactics concern the application of the tasks associated with offensive, defensive, stability, or defense support of civil authorities operations. Employing a tactic may require using and integrating several techniques and procedures. Tactics are contained in FMs. (TRADOC Regulation 25-36)

Tactics: the employment and ordered arrangement of forces in relation to each other

Update: The employment and ordered arrangement of the units in relation to each other is comprehended in the term, tactics. Maneuver is the term used to describe their movement in battle in relation to the terrain and to the enemy.

Procedures are standard, detailed steps that prescribe how to perform specific tasks (JP 1-02). They also include formats for orders and reports, and control measures. They are prescriptive. Procedures consist of a series of steps in a set order, and are executed the same way, at all times, regardless of circumstances, formats for reports, and specific control measures. Procedures require stringent adherence to steps without variance. An example is static-line parachute procedures. Parachutists follow specific steps in order when exiting an aircraft with a static-line parachute. Procedures are contained in the appendixes of FMs. (TRADOC Regulation 25-36).

Examples of procedures ...

Annex H format

Report formats

Troubleshooting procedures

Frequency assignment procedures

Signal operating instructions

Message format(s)

Telecommunications service orders 

Techniques are non-prescriptive ways or methods used to perform missions, functions, or tasks.  Techniques are contained in ATPs [not FMs!] (TRADOC Regulation 25-36).  Exception:  "Employing a tactic may require using and integrating several techniques and procedures." (See above definition of tactics).

Examples of techniques ...

Missions:  "Getting the message through"; Annex H to an operations order; commanders' critical information requirements; tanks and infantry integrating their actions at the small-unit level; patience and thoroughness in small unit armor tactics becoming more important than dash and speed; infantry learning to guide the tanks over the terrain, leading them around obstacles, pointing out enemy strong points, and actually protecting the tanks from hostile antitank weapons; tanks knocking out automatic weapons strong points located by the infantry and providing close-range fire support when infantry closes with the enemy; artillery observers advancing with the forward elements, enhancing the effectiveness of artillery fire against antitank positions and hostile batteries; and many, many others.

Functions:  mission command; intelligence; movement and maneuver; fires; sustainment; and protection; and others.  (Hey, they're called warfighting functions.)

Tasks:  (sources of) Universal Joint Task List; Army Universal Task List; Military Occupational task lists; etc.