Work to reinforce regular army policy (4)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

I think this is a quadruple definition, though I’m not sure of all of them. (1) as in one’s “line of work”, or the old TV programme What’s My Line? ; (2) to add a layer of fabric inside a garment to strengthen it; (3) the fighting forces of armies and navies, though this is a long way down the list of definitions in Collins; (4) as in “taking a hard line” on a particular issue.