Here's the overall feedback:
I appreciate that you made this in Scratch, which I find hard to do.
I like how the bullets just glide towards the bubble.
The bubbles also glide towards the tank.
The gliding is smooth, and the bullets, too.
--
The variables probably need more style, the background needs more visuals, and it would be better if I could hold LMB or space instead of spamming it. The game ends quickly, and I can't restart.