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The Harrier V/STOVL jet was designed in order for its users to be able to retain a functional air force even with all conventional airports destroyed; to this end, it can take off from, and land in, essentially any space large enough for it to fit into, potentially including unpaved dirt pads.

Unlike most jets designed to be capable of rough-field operations, the Harrier has no mechanism for preventing engine dirt ingestion, and, indeed, ingests considerable quantities of dirt and dust when operating from dirt fields:

Harrier ingesting dirt

(Image by @KeithS here at AvSE.)

How does the Harrier avoid engine damage from dirt ingestion during rough-field operations?

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    $\begingroup$ According to this RFP FOD ingestion for the AV-8B is a major problem. I'm guessing that they don't "avoid damage" so much as "deal with it when it happens". $\endgroup$
    – Ron Beyer
    Aug 31, 2019 at 3:58
  • $\begingroup$ I imagine putting the intakes so far forward is one way. $\endgroup$
    – acpilot
    Aug 31, 2019 at 6:59
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    $\begingroup$ From accounts I have heard of military operation of jet engines, running engines in a manner that shortens time between overhauls is not uncommon. $\endgroup$
    – J W
    Aug 31, 2019 at 10:20
  • $\begingroup$ @acpilot: And yet they still suck in lots of dirt, as shown in the picture. $\endgroup$
    – Vikki
    Aug 31, 2019 at 21:30
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    $\begingroup$ @acpilot, fore and aft doesn't have any effect, it's proximity to the ground and suction power. $\endgroup$
    – Michael Hall
    Feb 5 at 16:08

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How does the Harrier avoid engine damage from dirt ingestion during rough-field operations?

The short answer is that they don't. They avoid using these FOD-laden strips if possible, but doesn't have any kind of active method for reducing FOD damage from debris ingestion.

This is supported by an RFP that NAVAIR put out asking for proposals to reduce FOD for the AV-8B:

The AV-8B currently has the highest FOD damage rate in the U.S. DoD inventory which incurs a cost of more than $100M per year in engine removal, rebuild, and reinstallation, as well as decreased readiness and safety.

The method here is to just deal with it when it happens. The engine is removed, repaired, and replaced when a FOD incident occurs.

The document also says:

To date, NAVAIR has experienced more than eight Class 'A' mishaps in the AV-8B due to FOD

Where mishaps are defined:

Table - Current Mishap Definitions and Reporting Criteria

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