Mortar-style firing from 155 mm guns: accuracy, traverse and lateral deviations

The high-angle (mortar) trajectory in 155 mm howitzer fire is a mode used to engage targets behind terrain, in ravines, on reverse slopes and in dense urban areas. In this mode the elevation angle exceeds 60°, and the projectile follows a steep trajectory with a high apex.

This creates a specific problem: even a small traverse of the barrel in azimuth, for example 00-01 (1/60 of a degree), can cause a significant deviation of the point of impact in the lateral plane. This is especially critical at ranges from 8 to 15 km.

Why does the high-angle trajectory amplify the error?

In mortar-style fire the projectile flies along an arc-shaped trajectory. Its point of impact depends not only on the initial direction but also on the geometry of the arc — the steeper the angle, the greater the effect of even a microscopic traverse. Suppose the traverse was 00-01:

00-01 = 1 / 60 of a degree ≈ 0.01667° ≈ 0.000291 rad

According to the formula:

L = D × tan(α)

where:

• L — lateral deviation in meters,
• D — range to the target in meters,
• α — angular traverse in radians.

For a range of 10 km this gives only ~2.91 m, if firing along a flat trajectory. But in reality, in a high-angle flight, according to field observations, the deviation reaches 58–60 m (00-06).

This is because the point of impact is formed along a high arc, and a shift of even 0.0003 rad at the horizon is already tens of meters across the front.

Practical deviation values for a 00-01 traverse

In combat conditions, with a high-angle trajectory and ranges up to 15 km, the lateral deviation for a 00-01 traverse can be 20 times larger than in the theoretical model. The table is below:

Conclusions

• High-angle fire demands extremely accurate traverse of every gun, especially in battery fire.
• Fire control systems must take into account the flight geometry, elevation, wind by height and the Coriolis effect.
• For accurate engagement it is important to apply individual direction corrections for each SPG.

This ballistic feature is relevant for artillery systems such as the **M777**, **KRAB**, **AHS Kryl**, **Bohdana** and other high-precision platforms. Practical experience shows that even a 00-01 error when firing at high angles at 10–15 km is already a **potential miss** at the level of the target.