The skill, expertise, or quality of being an effective guerrilla fighter or practitioner of guerrilla warfare.
From 'guerrilla' plus the suffix '-ship', which forms abstract nouns indicating a state, condition, or quality of being or doing something.
Using '-ship' (like 'friendship' or 'leadership') to describe guerrilla expertise sounds a bit awkward to modern ears, but it shows how English created vocabulary to discuss unconventional warfare as a serious strategic discipline.
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