Crossword Puzzle Core groups begin operations?

Clue: Core groups begin operations?

Core military groups (CADRES with 6 letters)
Core groups (CADRES with 6 letters)
Core groups of potential leaders (CADRES with 6 letters)
Core groups? (NUCLEI with 6 letters)
Core groups of trained personnel (CADRES with 6 letters)
Impersonal notes ... or what four groups of this puzzle's answers do (totaling 11 words) (FORMLETTERS with 11 letters)
Corps core (CADRE with 5 letters)
Beginning of of relief? (SIGH with 4 letters)
Conclusion beginning (e.g. ANDSO with 5 letters)
Begin work, perhaps (PUNCHACLOCK with 11 letters)