In 1938, at the age of seventeen, Tabenkin joined the Field Squadron of the Haganah, an underground paramilitary organization operating in Mandatory Palestine.

In this final operation, he led his combatants to military victories, who, at that time, had gained the mastery of the field.

He was commander when, under directions from Moshe Dayan, a military unit specializing in biological warfare, contaminated the wells of Biddu and Beit Surik with diphtheria and typhus bacteria to prevent the dispossessed Palestinians in those localities from re-establishing themselves in their homes.

[5][6] In contrast, Operation Ha-Har was to open-up the Jerusalem Corridor south of Nahal Sorek, and to rid the area of all pockets of resistance.

After the war, Tabenkin studied industrial engineering at Technion University, where he earned a Bachelor's degree in 1961.