In the summer of 1937, as commander of the Jewish Settlement Police, he founded the Posh (פו"ש), the commando arm of the Haganah.

Sadeh commanded the establishment of Kibbutz Hanita on an isolated hill on the southern border of Lebanon.

[dubious – discuss] The purpose of this clandestine elite unit was to prepare to undertake a guerilla war in the event of the Axis powers entering Palestine.

[2] He was Commander of the Palmach until 1945, when he was appointed as the Haganah's Chief of the General Staff, and among other activities was in charge of the movement's operations against the British Forces during the remaining years of the British Mandate of Palestine and in [Aliyah Bet| operations that brought clandestine Jewish immigrants]] to the country.

In early April he successfully defended the kibbutz against a full-scale attack by the Arab Liberation Army (ALA).

At the end of April he commanded two brigades in a series of attacks on strategic areas in and around Jerusalem, Operation Yevusi.

The book Misaviv Lamedura (Around the Bonfire) includes a collection of articles he wrote under the pen name Y. Noded (Y. Wanderer).

Thousands of sportspeople and soldiers now take part in the Mount Tabor Race, devoted to Sadeh's ideals.