Active Protection (APS)

Work in progress

This wiki is still being written. Pages are incomplete, numbers may change, and some mechanics are not covered yet.

An Active Protection System intercepts an incoming round inside its arc. Chemical shells detonate early, while kinetic rounds survive with a calibre-based cut to their penetration.

What an APS does

An Active Protection System watches for an incoming round inside its arc and fires an interceptor at it. What happens next depends entirely on whether the incoming round is chemical or kinetic, and the two outcomes are very different.

Incoming	Result of an interception
HEAT, ATGM, HE and other chemical	Detonates at the intercept point, well short of the armour
AP, APDS, APFSDS, kinetic missiles	Survives, but loses a share of its penetration

Key idea

A kinetic round is never destroyed by an APS. It keeps flying and still hits, just with less penetration behind it.

The penetration cut

The amount a kinetic round loses depends on its calibre and on the system's degradation factor $F$ , which is always at least 1. Larger calibres keep much more of their penetration.

P \leftarrow \dfrac{1}{F}\cdot\begin{cases} \min\!\left(\frac{C}{80}P,\ P\right) & \text{AP, APDS} \\[4pt] \frac{C}{C+20}\,P & \text{APFSDS, kinetic missiles} \\[4pt] \min\!\left(\frac{C}{110}P,\ P\right) & \text{other} \end{cases}

C is the calibre in mm and P the penetration the round had on arrival.

Round	Calibre	Penetration kept at F = 1
APFSDS	120 mm	about 86 percent
APFSDS	60 mm	about 75 percent
AP	80 mm	about 100 percent
AP	40 mm	about 50 percent
AP	20 mm	about 25 percent

Large darts shrug the system off. Small calibre AP is nearly erased by it.

Coverage

Each launcher covers a horizontal and a vertical sector out to a protection radius. A round arriving from outside that cone is never engaged in the first place.

Horizontal View ⟷ -70° to 70°

Vertical View ↕ -10° to 40°

Top down and elevation arcs for a 140 degree front system

The same coverage as a dome, drag to orbit

The values that define a system

Launchers

count

Charges available before it runs dry

per unit

The system stops working once destroyed

Radius

metres

How far out it can engage

Reaction

seconds

Delay between detection and firing

Degradation

factor

Divides the penetration a kinetic round keeps

Anti-airburst

yes or no

Whether it also defeats airburst rounds

Note

A round that arrives faster than the reaction delay is never engaged, and launchers are finite, so a system can be emptied.

Where this fits in the pipeline

Note

The penetration cut above is the only place an APS touches the damage pipeline. Once a round is past it, everything else follows the normal rules on the penetration page.

Active Protection (APS)

What an APS does #

The penetration cut #

Coverage #

The values that define a system #

Where this fits in the pipeline #

See also

What an APS does

The penetration cut

Coverage

The values that define a system

Where this fits in the pipeline