U-BOAT KILLER v. 1.0.2
Destroy the enemy submarines!

(C) JCCyC 2026
A game for the TRS-80 Color Computer 1 and 2


1. WHAT IS THIS GAME?

U-boat Killer is a remake of "Depthcharge", the arcade game Gremlin
released in 1977. You command a destroyer on the surface of the sea.
Below you, enemy U-boats cross the screen at five different depths.
Drop depth charges on them, sink as many as you can before time runs
out, and stay clear of the mines they release.

This is the Color Computer version of the MSX game of the same name. It
plays exactly the same and looks the same, in the CoCo's black and
green high-resolution mode. Its sounds are a fanfare on the title
screen, explosions, and a blip for each figure cashed in at the end
of the game.


2. WHAT YOU NEED

- A Color Computer 1 or 2 with at least 32 KB of RAM and a disk drive
  (Disk Extended Color BASIC). The game was tested on emulated 60 Hz
  machines (CoCo 1 and CoCo 2B, as sold in the USA) and on 50 Hz
  European ones.
- The disk image UBKILLER.DSK.
- The keyboard. The game doesn't use joysticks.


3. HOW TO RUN IT

On a real Color Computer:
  Write UBKILLER.DSK to a floppy disk with a disk image tool, or use it
  from a CoCo SDC or DriveWire. Put it in the default drive (normally
  drive 0) and type
        RUN"UBKILLER"
  or, without the small BASIC loader,
        LOADM"UBKILLER":EXEC

On a PC, Mac or phone, with an emulator:
  Any CoCo emulator with a disk controller can run it: XRoar, MAME and
  others. Insert UBKILLER.DSK in drive 0 and type RUN"UBKILLER". With
  XRoar, for example:
        xroar -machine coco2bus -load-fd0 ubkiller.dsk


4. CONTROLS

  Move the destroyer left/right .... Left and right arrow keys
  Drop a charge off the LEFT side .. Z
  Drop a charge off the RIGHT side . X
  Start a game ..................... Space bar
  Pause / resume ................... P

The destroyer moves while you hold the arrow key and stops when you let
go. Each press of Z or X drops one charge.

P pauses the game: everything stops and "PAUSED" shows at the top,
where the charge squares were. Press P again to carry on.


5. STARTING A GAME

When the game starts, the title appears one line at a time. When
"PRESS SPACE TO BEGIN" starts blinking, press the space bar to play. If
you wait, the title and the high score list take turns on the screen;
you can start from either one.


6. THE SCREEN

Along the top, from left to right:

  TIME       The time left in the game. It counts down from 89.
  Squares    Six little squares show how many depth charges you can
             still drop. One disappears when you drop a charge and
             comes back when that charge is gone.
  SCORE      Your score.

Below that is your destroyer, sailing on the surface. The dark sea
below holds the submarines, on five depth levels. At the very bottom,
a tally shows a little figure for every sub you sank and every time
your destroyer was sunk.


7. HOW TO PLAY

The submarines
  Subs cross the screen from side to side, never more than one on each
  depth level. The deeper a sub, the more it is worth, and the slower
  it moves:

    Level 1 (shallowest) ... 10 to 30 points ... crosses in 10 seconds
    Level 2 ................ 20 to 40 points ... crosses in 20 seconds
    Level 3 ................ 40 to 60 points ... crosses in 30 seconds
    Level 4 ................ 60 to 80 points ... crosses in 40 seconds
    Level 5 (deepest) ...... 70 to 90 points ... crosses in 50 seconds

  Each sub shows its value on its hull. The game starts with two subs
  at a time. When the clock reaches 55 a third one joins in, and at 20
  a fourth.

Depth charges
  A charge is thrown in a short arc off the side of your ship, lands on
  the water and then sinks slowly, spinning, all the way to the seabed
  (it takes 19 seconds). If it touches a sub on the way down, the sub
  is destroyed and you score its points. A charge that reaches the
  bottom explodes there, and the explosion can still catch a sub on the
  deepest level.

  Some rules:
  - At most six charges can be in play at once.
  - Each side can drop one charge per second. The left and right sides
    are independent, so you can drop one on each side at the same time.
  - You can't drop a charge that would fall off the edge of the screen,
    so move away from the edge first.
  - Aim ahead of the sub! Charges sink slowly, so drop them where the
    sub is going to be, not where it is now.

Mines
  The subs release mines that float up to the surface. A mine that
  reaches the surface anywhere under your destroyer, even under the tips
  of the bow and stern, blows it up.
  Any other mine just bursts harmlessly on the surface. Watch the
  water below you and move out of the way.

Losing your destroyer
  When a mine hits you, your destroyer sinks and you lose HALF YOUR
  SCORE. A new destroyer appears in the middle a moment later. There is
  no limit on how many ships you have; the only enemy that ends the
  game is the clock.

Time and overtime
  A game lasts about 112 seconds. If, when time runs out, your score is
  600 or more, you get OVERTIME: the word OVERTIME flashes, the clock
  restarts at 45 and you keep playing.

End of the game
  When time is up, everything freezes and the tally at the bottom is
  cashed in, one figure at a time: every sub you sank is worth a BONUS
  OF 30 POINTS. Destroyer figures are removed too, but give nothing.
  Each figure goes with a blip.


8. HIGH SCORES

The ten best scores are kept, with the initials of whoever made them.
If your final score beats one of them, you are asked to ENTER YOUR
INITIALS:

  - Type up to three letters and press ENTER. CLEAR takes one back.
  - Or press the left or right arrow to choose a letter (right starts
    at A, left at Z) and the space bar to take it; taking the third
    one finishes. The down arrow takes one back, and the up arrow
    finishes with fewer.

One or two letters are fine too, but you need at least one. The game
saves the high scores in the file UBKILLER.HSC on the default drive
(normally the disk it started from) each time a new score enters the
table, and loads them when the game starts. If the disk is
write-protected or can't be written, the scores still last until the
computer is switched off. To start over from the original table, KILL
"UBKILLER.HSC".


9. TIPS

- Deep subs are slow and worth a lot, but your charges take a long
  time to get there. Shallow subs are fast but easy to reach.
- Dropping charges on both sides at once covers more water.
- Don't run out of charges: they only come back when the old ones are
  gone, and a charge sinking to the bottom stays in play for a long
  time.
- Losing your ship costs half your score, so near the end of a good
  game, keep an eye on the mines.
- Reaching 600 points before time runs out pays big: overtime gives
  you about 56 more seconds with four subs on screen, and the bonus
  keeps growing.


Have fun, and good hunting!
