Even though I don't even think I'm halfway through the season at this point, I've got the worrying feeling that the number of episodes where Briggs is either sidelined or just in a supporting role are starting to outnumber the ones where he's front and centre as the main character.
By my count, there are 20 episodes where Dan is part of the mission team, 7 where he just briefs/supervises the team from home, and one where he's completely absent. The latest episode you mention having seen, the Lloyd Bridges episode ("Fakeout"), is episode 12 in broadcast/DVD order; of the remaining 16 after that, Dan is on the team in 11. I'm not sure how central he is in those, though. There is one episode ("Shock") where he's the central team member but spends most of the episode in a mask and is therefore played by James Daly instead of Arthur Hill.