The IDF was established on 31.5.1948. Until then the Hagana's General Staff, its units, commanders and combatants fought in the War of Independence. The Hagana's contribution to the IDF is evident in all aspects, and its principles and methods are in use to this day. Hagana commanders developed various tactical methods in accordance with the Yishuv's ever changing needs, and adapted them to the ever changing circumstances. The Hagana operated as the Zionist movement's armed force, defender of lives, property and implementer of the Zionist dream. Back in the 1920's Hagana members engaged in the defense of their own settlements.
When attacked, members defended their own homes. Training programs only included the use of fire arms, drills and physical training.
The 1939 Arab Riots or uprising brought about drastic changes in the Hagana's operating methods, with the Hagana engaged beyond the perimeter of the settlements, near their houses.
Training and instruction systems developed as well. Squad and platoon commanders training programs expanded in the beginning of the 1930's. Professional courses which included sabotage, reconnaissance, wireless communications, weaponry etc., contributed to the formation of the Hagana's combat doctrine and military thinking, which was passed on by course graduates to future generations of commanders.

Development of Military thinking and strategy:
Phase 1- Passive defense of human life and property.

Phase 2- Regional Defense- based on mutual assistance among settlements, and securing roads and communication.

Phase 3- Active Defense- mutual defense.
Perimeter defense, ambush and retaliation activities in enemy territory and defensive operations outside the domain of the Jewish settlements.

Phase 4- Occupation of territory and "Enemy annihilation"- General Staff hierarchy - region, district and area.
Motorized forces - Hish and Palmach. Development of combat strategies: Commando fighting, Night fighting, Platoon & company armed combat.
Strategically planned Settlements, designed to facilitate the occupation of new regions. Yishuv defense plans (Avner Plan and Plans A-C), operative planning for the occupation of territories designated for the State of Israel, Plan D - Sabotage of enemy army bases, cities and forces.

Phase 5- Offensive phase- Hagana evolving into the IDF - invasion containment, defensive and offensive strategies and assaults.
Strategic initiated assaults aimed at expelling and annihilating the invader, and re-occupying Israeli territories.

Turning points in Hagana operations, in terms of the organizational structure:
* Establishment of National Command in 1931- the organization becomes national.
* Offensive operations outside the domain of the Jewish settlements, 1936.
* Jewish agency appoints the Head of the National Command and subordinated it to its authority. The Hagana becomes a national defense organization under the direction of the Zionist Movement.
* Establishment of the General Staff in 1939 - the Hagana begins to perceive itself as the army of "the state in the making".
* Establishment of the Palmach in 1941- creation of a nationally mobilized force.
* 1944- Hagana forces are organized (Palmach, Hish, and Chim) into battalions.
* 1947- Palmach and Hish forces form brigades and Chim forms regional forces.
* Establishment of General Staff; logistics; manpower and training branches.
* Hagana promotes night combat doctrines. Main offensive operations carried out during the War of Independence, first by Hagana and later by the IDF, were carried out under cover of night due to enemy superiority and the efficiency of night operations. The IDF carried out day time assaults only towards the end of the war.