The Arab Riots of 1939 presented the Hagana with new problems. The uprising, aimed mainly at the British, lasted for a long time. Contrary to previous attacks, road transportation and farmers were attacked as well.
The Hagana utilized its experience in fighting the Arab uprising to increase its quantity and quality. At the initiative of local commanders, such as Yitzhak Sade and Eliyahu Ben-Hur, complex "Outside the Fence" operations were perfected. These tactics, stemming from previous beginnings in the development of the Hebrew defense force, were based on initiating offensive operations in the areas between settlements. For the first time, forces set out to lay ambushes and wait for the enemy outside settlement fences and near their bases, Thus, they undermined the enemy's confidence in their movements both during the day and night.
Yitzhak Sade established the Hagana's Field companies (Fosh), a national trained mobile force "assigned to reinforce areas prone to attack, carry out preventive action, patrol and pursuit: (Yitzhak Sade) against known enemy targets, avoiding action against civilian population according to the 'policy of restraint' decided upon by Yishuv leaders.
As a result, many joined the Notrim, the British police auxiliary force. The Notrim were the only members of the Hagana recognized by the British, while the rest of the organization was considered illegal.
By the summer of 1939, the Notrim numbered 22,000, and owned 8,000 guns. 4,300 Notrim were fully enlisted, 15,000 were partly enlisted and 2,200 served as special policemen. The Notrim's weapons and battle experience was central to the success of Hagana units.
The establishment of the Special Night Squads (SNS) under the command of Charles Ord Wingate was the result of the successful collaboration between the British army and the Hagana. The squads included British soldiers and Fosh members, operated under cover of the night, against armed Arab gangs in Emeq Yizra'el. The squads patrolled during the night and operated as "mobile ambushes". Wingate was known as the 'Yadid' - (the Yishuv's friend); his combat methods were taught and used both in Hagana and the IDF.
Dozens of Stockade and Watchtower (method of building new agriculture settlements in the 1930's, during the Arab Rebellion in Palestine) settlements were founded during the Arab riots of 1939. The Hagana planned the settlement map, helped build the settlements and was responsible for their defense.
During this period, 350 Hagana members were killed in action.
The Hagana emerged from the riots of 1936-1939 as a strong military organization, forming its defense strategies, combat and training methods. The Hagana's General Staff was established in 1939, and a Chief of Staff was appointed as a professional military commander, taking the Hagana one step further to become a full fledged army.