I was on a construction site in Florida about 10 years ago, a new
powerplant, actually, when one of the major subcontractors called the
local union business agent to tell him he need five more workers
beginning the next day and continuing for a number of weeks.
"Send me the graybeards," I recall him saying, "I want guys who know how
to do it right the first time, without supervision."
When it is critical, seniority counts.
Seniority in a union just means you have managed to stick around for a
long time. It says nothing about the quality of your work or your
competency.
Seniority in the marines just means you re-enlisted.