[1][2][3] The formation of ON was the product of discussions among senior officers of the Army and Ministry of Defense that took place immediately after the Nazi occupation in March 1939.
As early as March 19, some of the senior officers in the Czech army, including Gen. Sergej Ingr, Gen. Josef Bílý, and Gen. Sergei Wojciechowski, began talking about establishing a military resistance organization.
The original goal of fomenting an uprising against the Nazi occupiers power was soon abandoned as the ON became more focused on intelligence gathering and then on carrying out minor acts of sabotage.
During the Nazi occupation, many ON officers secured jobs at companies involved in strategic production, such as the Škoda factory in Plzeň.
After the fall of Nazi Germany, ON hoped to serve as the Army of the restored Czechoslovakia and to maintain civil order until the return of political leaders from exile; but it proved difficult to secure the number of weapons necessary for these purposes.
Between June 1939 and the end of the summer of that year, 200 battalions and command structures had been formed, and by August members ON had managed to penetrate the Gestapo.
At first, leaders of the second iteration of the ON sought to re-establish it as an underground army, but as it became clear that the war would last longer than expected, they abandoned the idea of having a large, tightly structured organization.
Heydrich died in June 1942 as a result of complications following an assassination attempt, and this triggered another round of ON arrests, which in effect destroyed the second iteration of the group.
In 1943–44, a military movement under the direction of Gen. Zdeněk Novák was formed, but this group was virtually destroyed in a June 1944 strike by German security forces.
By this point, ON bore virtually no resemblance to its first iteration: it had no unified command or hierarchy, and its cells were only loosely associated with one another, a state of affairs which minimized the danger that a single arrest would lead to many others.