The hammer in Wrecking Crew.. is tricky. Back when the game was first out I played it a LOT determined a couple things:
- You need to explode 3 bombs - the last being the most important and does not change from game to game.
- You need to swing the hammer XX amount of times to explode those 3 bombs. This in my discovery varies from 3 to 10 swings.
The best/easiest example of this I can give is obtaining the hammer in 3 swings on level 6:
Smash the bombs in that order - it doesn't really matter with the first two, but number 3 should be last. You can only take 3 total swings to do this.
If all goes well, you'll get this:
Simply swing on the hammer icon that comes out and you'll have the Golden Hammer. This is a fast swinging hammer will break all walls with one swing (even the darker ones that require 3 hits normally). It can even disable and knock down enemies if timed correctly. The hammer will stay with you until you die and can be used for multiple levels.
Enjoy!