So I'm on to the second mission of the campaign. I have to place a demolition charge. I googled and read that if you select the demolitions guy and move him to the appropriate place, the sight changes and then I guess you do "use." This, alas, isn't working for me - the sight doesn't change. Who'd like to spell it out?

you probably figured it out by now but you switch to the secondary weapon by pressing the ~ key and then you walk up to it and press the fire button to place the charge. just leave it and it will blow at the end of the mission.

Rejoice! I hadn't worked it out for myself. After posting, I noticed there'd been no activity here for months, and I feared I wasn't going to get a reply this year. I give you fulsome thanks.

This came at just the right time. The first time I had this problem, blowing something up was an optional objective, so I missed it out, but within the last half hour I got to a mission where it was a key objective.