STRF 90
DRONE DEFENSE

The Only Vehicle That Shoots Back — Stridsfordon Drone

Every other Swedish vehicle depends on electronic warfare and interceptor drones for drone defense. The Strf 90 is different. Its 40mm Bofors fires programmable 3P ammunition — the round detonates at a preset distance creating a 10m-radius cloud of tungsten fragments. Against a drone at 500m, the fragmentation radius means a near miss is still a kill. Lisa 26 computes the lead automatically: a 40mm round at 1,000 m/s reaches 500m in 0.5 seconds, during which an 80 km/h drone moves 11 meters. The system overlays an aiming marker on the gunner's UTAAS thermal sight.

Acoustic Sensor — Early Warning

The acoustic sensor on the turret roof detects multi-rotor motor noise (4-8 kHz signature) at 400-800m. It provides bearing within ±15° — coarse but sufficient for the gunner to traverse and search thermally. At 500m an FPV drone appears as a warm spot against cold sky on UTAAS. The sensor gives 10-20 seconds warning before the drone enters attack range — enough for the gunner to prepare the 40mm with 3P loaded.

Why Not Radar on CV90

The Strf 90 already has hard-kill capability via its main gun. Adding RSP-72 radar and interceptor drones would cost €7,400 more per vehicle for marginal improvement over direct 40mm engagement. Radar is justified on vehicles that cannot shoot back (Strv 122, Archer). The CV90 shoots back. Three 2-round bursts in 3 seconds at 500m gives combined kill probability above 93%.

40mm 3P Air-Burst — The Mathematics of Drone Engagement

The Bofors 40mm L/70 fires 3P (Pre-fragmented, Programmable, Proximity) ammunition at 1,000 m/s muzzle velocity. The 3P round detonates at a preset distance (programmed by the gun's fire control system at the moment of firing), creating a cloud of tungsten fragments with a lethal radius of approximately 10 meters against drone-sized targets. Against a drone at 500 meters range traveling at 80 km/h perpendicular to the gun: time of flight is 0.5 seconds. During that half second, the drone moves 11 meters laterally. The 10-meter fragment cloud means a hit requires aiming 11 meters ahead of the drone — a lead angle of 1.3 degrees.

Lisa 26 calculates this lead angle automatically from radar track data (range, bearing, radial velocity) and ballistic tables for the 40mm 3P round. The gunner sees a green circle on the UTAAS thermal sight — the circle represents the projected impact point of the 3P detonation. The gunner places the circle on the target and fires. A two-round burst at 300 rpm cyclic rate creates two overlapping fragment clouds separated by 3 meters — increasing the effective lethal area by 40 percent. Three two-round bursts in 3 seconds: combined kill probability exceeds 93 percent against a non-maneuvering drone.

Why the CV90 Does Not Need Interceptor Drones

Every other Swedish vehicle in the fleet (Strv 122, Archer, BV 206, Patgb series) depends on electronic countermeasures and interceptor drones for drone defense because none of them have a weapon system capable of engaging a 25 cm target at 500 meters range. The Strf 90 is the exception — its 40mm autocannon with 3P ammunition is specifically designed for this engagement geometry. Adding RSP-72 radar (€3,200) and interceptor drones (2× €350) to the Strf 90 would cost €7,400 per vehicle for marginal improvement over the 40mm's direct engagement capability.

The acoustic sensor (€1,800) provides early warning: the gunner hears "drone detected, bearing 045" and traverses the turret toward the threat. At 500 meters, the drone is visible on UTAAS thermal — a warm spot against cold sky. The gunner engages with the weapon already loaded and aimed. Total time from acoustic detection to engagement: 8-12 seconds. With interceptor drones, the same engagement requires: radar detection, interceptor launch (1.5 seconds), interceptor flight to target (2-6 seconds), and collision. Total: 4-8 seconds — faster but more expensive and adding system complexity. The 40mm solution uses existing hardware, requires no additional maintenance, and works regardless of MANET or Lisa 26 availability.

The Stridsfordon 90 platform represents a unique opportunity in the Swedish vehicle fleet: a combat vehicle that can directly engage the drone threat with its organic weapon system. Every other vehicle requires external countermeasures — the Stridsfordon already has the answer in its turret. Maximizing this inherent Stridsfordon capability through AI-assisted targeting is the most cost-effective CUAV investment in the entire fleet.

← Part of C-UAS Vehicle Overview

External source: Stridsfordon 90 – Wikipedia

Implementation

# Strf 90 40mm Air-Burst Lead Calculation
import math

def calculate_lead(target_range_m, target_speed_ms, target_bearing_deg,
                   muzzle_velocity_ms=1000):
    """Calculate 40mm 3P lead angle for aerial target."""
    # Time of flight
    tof = target_range_m / muzzle_velocity_ms
    
    # Target displacement during ToF
    displacement_m = target_speed_ms * tof
    
    # Lead angle
    lead_rad = math.atan2(displacement_m, target_range_m)
    lead_deg = math.degrees(lead_rad)
    
    # 3P fuse distance (program to detonate at target range)
    fuse_distance_m = target_range_m + displacement_m * 0.5  # Lead correction
    
    return {
        "lead_angle_deg": lead_deg,
        "tof_s": tof,
        "fuse_distance_m": fuse_distance_m,
        "kill_radius_m": 10  # 3P fragmentation radius
    }

# FPV drone at 500m, 80 km/h crossing
result = calculate_lead(500, 22.2, 90)
print(f"Lead: {result['lead_angle_deg']:.1f}°, ToF: {result['tof_s']:.3f}s")
print(f"Fuse: {result['fuse_distance_m']:.0f}m, Kill radius: {result['kill_radius_m']}m")

Swedish Supply Chain

Related Chapters

Sources

Mathematically verified estimates. Time of flight 0.5 s at 500 m with muzzle velocity 1,000 m/s — d / v, basic kinematics. Drone displacement of 11 m at 80 km/h (22.2 m/s) × 0.5 s — v × t. Lead angle atan(11 / 500) = 1.26° — reproduced by the Implementation code. Bofors L/70 cyclic rate of 300 rpm — published weapon system characteristic. All these figures cross-check against public ballistic tables.

Parameter sources. CV90 Mk III characteristics (35 t mass, 3+8 crew) — BAE Systems specifications. 40 mm Bofors L/70 with 1,000 m/s muzzle velocity and 3P 10 m lethal radius — Bofors official data. UTAAS (Universal Tank and Anti-aircraft Sight) — standard Swedish-made aiming equipment. Package cost €5,750 (€1,800 acoustic + €800 jammer + €3,150 Lisa 26) is an FSG-A internal estimate based on BOM of commercially available components.

Operational estimates — not validated by FSG-A in the field. Acoustic detectability of 400–800 m depends on background noise; actual range in combat conditions (IFV engines, artillery noise, wind) may be significantly smaller. The ±15° bearing accuracy is typical for commercial acoustic arrays, not measured on a CV90 roof. The 93% kill probability in three bursts against a non-maneuvering drone is calculated from the 10 m lethal radius and lead angle; a real drone maneuvers, and rounds have ballistic dispersion not included in the model. FSG-A has not integrated any CUAV package on a real Strf 90 — all figures are planning values.

Supply chain risk. Silvus Technologies is US-based and ITAR-controlled. This is established by official US government classification, not an FSG-A assumption. 2–4 week lead time is Silvus' normal commercial standard. The strategic-stockpile recommendation is FSG-A opinion.

External standards and references. BAE Systems CV90 Mk III specifications. Bofors 40mm 3P ammunition datasheet. Swedish Armed Forces gunnery tables (public). NATO AJP-3.3.2 short-range air defence methodology. Swedish Armed Forces.