Sub-subunit
Subunit or sub-unit – subordinated element of (bataillon sized) parent units identified in authorization documents by name, number, or letter; e.g., companies or battalions, platoons or detachments of separate companies.
Typical subunits are:
-infantry company
-artillery battery
-U.S. Cavalry troop
-Commonwealth armor or combat engineering squadron [Military Wiki]
In most branches of the army, the sub-unit is the smallest formation that can support itself. Sub-unit command is often the first time you have subordinate officers and staff (small though it is). And subunit command offers an unprecedented level of freedom [Meddings M.W.].
Subunit. Military Wiki. Retrieved from: https://military-history.fandom.com/wiki/Subunit_(military)#cite_ref-1
Meddings M.W. (2018). What Got You Here Won’t Get You Further: On Success, Culture and Communication. Retrieved from: https://thearmyleader.co.uk/sub-unit-success-culture-communication/