What is Arsenal?

Legal Definition
An arsenal is a place where arms and ammunition are made, maintained and repaired, stored, or issued, in any combination, whether privately or publicly owned. Arsenal and armoury (British English) or armory (US spelling) are mostly regarded as synonyms, although subtle differences in usage exist.

A sub-armory is a place of temporary storage or carrying of weapons and ammunition, such as any temporary post or patrol vehicle that is only operational in certain times of the day.
-- Wikipedia
Legal Definition
Store-houses for arms; dock-yards, magazines, and other military stores.
-- Black's Law Dictionary