SILENT RUNNING (1K ZX81)
by S A Nicholls, Keynsham, Bristol
from Your Computer (March 1982), Pages 65-66

This flicker-free game program is written for the ZX-81 in machine code. It
is only suitable for machines with from 1K to less than 3.5K RAM, because
of the way the background is printed.

The object of the game is to hit a submarine with a depth charge in the
shortest time possible. The display occupies the full screen. Movement of
your ship is controlled by key 5 for left and 8 for right. The ship has
twice the speed of the submarine. A depth charge is dropped by pressing the
0 key.

The display has a counter which starts at 999 and counts down in ones to
zero in roughly 25 seconds. The game finishes when the counter reaches zero
or when a submarine is hit, at which point the counter will stop at your
score. The submarine travels from right to left and its speed decreases
continuously as the game progresses to give more time to hit it. The first
pass takes approximately one second.

The depth of the submarine also increases with each pass of the screen.
When it reaches the sea-bed the next pass will be at the top of the sea and
so on.

[Note this program only runs on an edition 1 ROM ZX81. It can be converted
to run on an edition 2 ROM by modifying it as follows:

        POKE 16586,29
        POKE 16591,26
PF]