Thankfully, a little extra digging reveals more details about this tactic.
"Experience of direct fire by rocket artillery in the streets of Berlin
In street battles, when a solid front line is gone and enemy units are often found in individual houses and crossroads, the use of traditional artillery is impossible. Rocket artillery units used M-13, M-31 and captured 280 mm rounds to fire directly without launchers.
Considering the caliber and destructive force of M-31 rockets, their use was an effective measure against enemy concentrations.
Rockets were used to destroy all or parts of houses that contained enemy concentrations or impeded progress. The conditions of city fighting allowed for transport and installation of rockets 30-100 meters from enemy forces in a house window or wall breach. Aiming was performed with a primitive aiming device.
The effectiveness of M-31 rockets is achieved due to the following:
- At short distances (30-100 meters), it is possible to hit a small target such as a smokestack, church cupola, window, or breach in a wall. Due to the destructive power of the rocket, the target is completely destroyed.
- Using rockets to fire directly at the last minute allows our forces to eliminate the enemy or clear a path before the enemy has a chance to commit mobile reserves. The sudden and complete destruction has a great effect on enemy morale.
- There are concealed paths towards to front lines.
- The target is 30-150 meters away.
- The placement of rockets is done secretly and silently.
- Cooperation with infantry is carefully and correctly carried out.
Horizontal aiming was performed with a primitive sight, consisting of one nail in the front of the mount and two nails in the rear. Vertical aiming was performed by stacking bricks and wooden beams under the rear of the mount. The mount was stabilized with wire in different directions. This held the mount in place during the process of firing, which improved accuracy.