Allan McGregor, Maynor Figueroa and Curtis Davies have all signed up at the KC Stadium, while permanent agreements have been struck for former loan stars Ahmed Elmohamady and George Boyd.
Bruce has been left frustrated in his pursuit of attacking firepower, with a move for Burnley striker Charlie Austin collapsing on Tuesday on the back of a failed medical.
The Tigers boss is, however, pleased with how his squad is shaping up ahead of a return to Premier League competition in 2013/14.
Bruce told the club's official website: "So far, we have brought in three quality players to add to the existing squad.
"We will be doing our best to add more to that, and we aren't finished yet by any stretch of the imagination. We will keep working away at it.
"We have also turned a couple of last season's loans into permanent deals in Ahmed and George and that was important.
"Elmohamady was our Player of the Year last season, so the first piece of important business was to get his transfer over the line and we did that, in the same way that we secured [Robbie] Brady and [David] Meyler midway through last season.
"We are very pleased with what we have got so far. We will add one or two more to make us bigger, stronger and better, and to make us better equipped for the challenge ahead."