Needs to have dismissal of one hundred extras (9)

'extras' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Perhaps there's an association between them I don't understand?

'needs to have dismissal of one hundred' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'hundred' could be 'a' (synonyms) and 'a' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?