MechWarrior 3 Rebuild

MechWarrior 3 Rebuild

An unofficial fan rebuild of MechWarrior 3 (Zipper Interactive and MicroProse, 1999) for today's computers: Windows 10 and 11, macOS and Linux, with no Wine, DirectX wrappers, DDrawCompat or dgVoodoo.

It is not a remake. The original Mech3.exe (patch 1.2) was taken apart and its code rewritten function by function in C++, most of it checked against the original running in an emulator. The game plays the way it always did, minus the bugs and the problems it has on modern machines. It is a personal learning project: free, not sold, and not affiliated with or endorsed by Microsoft or MicroProse.

No game files are included. You need your own copy of MechWarrior 3.

Found a bug? Please report it.

What's new

Every release's full notes are on the Releases page, and CHANGES.md lists everything the rebuild changes from the original.

Coming in the next release

• The same acceleration above 83 fps. Holding a throttle key above about 83 fps skipped the mech's slow build-up of speed, so it pulled away nearly 2 seconds sooner than at 30 or 60 fps. It now builds up the same at any frame rate.
• Walking into a building does its full damage at any frame rate. An earlier fix scaled the 20 damage of each touch by the frame time, so the higher your frame rate the less a building took (about a fifth at 144 fps). Each touch does 20 again, as in the original.
• Where a foot reads the ground. The original never filled in the setting that decides when a foot uses the ground under its middle. Our fix guessed at it; it now uses the value the original team's own Pirate's Moon sets. This changes slightly how feet sit on slopes and when a foot counts as in water. This is part of bug fixes.
• The target keys tell the HUD again. Choosing a target with E, W or their Ctrl and Shift forms now does what Z and Q already did: the target triangle pulses, the target's mech sound plays, and a missile lock starts over on the new target instead of carrying across.
• A stick's throttle lever stays the right way round. Tapping throttle-down with the lever below stop, or pressing Toggle throttle direction (Backspace or stick button 10) with it above stop, could leave the lever backwards until the mission ended. That toggle no longer affects a lever. If yours runs backwards from the start, use the Invert box (Options, Controls, Assign Axis).
• Op 2 Mission 2's gas kills. After the Air Refinery goes down, standing in its gas now destroys you, or Dominic, as the original does; before, nothing happened.
• The debriefing's scores. A campaign debriefing now lists the mission's objectives, each worth 2500 when done, and counts them in the mission and campaign totals and the rank; before, it listed none and scored none. Instant Action's Battle Waves and Progression now score 1000 a wave plus a bonus for how far you got, as the original does, in place of a flat 1000, so a round that clears no wave scores nothing but its kills. Scores you already have stay as saved; new missions add to them.

1.0.3 (2026-11-05)

• Your data folder can live on another drive: GAME FILES, MY DATA FOLDER in the launcher copies it, checks the copy, then switches over, and removes the old copy only if you say so. If the drive is missing at start the game says so instead of starting afresh.
• Linux: the game no longer closes at the end of the intro movies.
• Linux: an install in any letter case now works (all lower case, all upper case, or mixed).
• A softer message for mods: when files match neither 1.0 nor 1.2, it now says data mods are read, though they may not play right, and that a mod which patches the old Mech3.exe won't apply. It never stopped the game.
• Crashes say why: a crash or a failed start now leaves a line in the log and shows a message box, on every platform.
• Windows: the installer asks for a folder every time, so you can install somewhere other than C.
• Vehicles on fast machines: small bumps throw them much less. On rough ground they still tip more than at 30 fps, and they still jump off steep banks at full speed, as in the original.
• A band under the sky: where nothing is drawn between the far ground and the sky, the game now shows the fog's colour.
• Smaller fixes: a memory leak in the zoom views, a light's position, and the pitch of moving sounds.

1.0.2 (2026-11-04)

• Lancemates walk round things. When a straight walk fails, they find a way round walls, up ramps and across rivers. Part of bug fixes; not for enemies or in multiplayer.
• Lights made during play work. Jump jets and gunfire light your mech.
• A mech no longer walks by itself when saved stick controls are used with no stick attached.

1.0.1 (2026-11-03)

• Op 1, Mission 2's missile platforms no longer vanish at high frame rates, which could make the mission impossible to win.
• Custom key bindings work on the Controls screen.
• Flight sticks: twist and throttle reach the right axes, and the throttle lever reaches reverse.
• A crash late in a fight is fixed, along with the end credits on wide screens and the mech lab's "Overwrite?" box.

What you need

• Your own MechWarrior 3, any of these:
  • an installed copy, version 1.2 or 1.0 (the rebuild makes the 1.2 patch's changes itself as 1.0's data loads, so it plays as 1.2; your files are not changed);
  • the original disc;
  • a disc image: an .iso, or a .cue with its .bin files (a .cue also gives you the music).
• A computer with a graphics card that does Direct3D 12 (Windows), Metal (Mac) or Vulkan (Linux):
  • Windows 10 or 11, 64-bit;
  • macOS 12 or later, Apple silicon or Intel;
  • Linux, x86-64, with your distribution's Vulkan driver.

Pirate's Moon is not supported yet.

Download

From the Releases page:

	File
Windows	MW3-Rebuild-Setup-<version>.exe	An installer. A .zip of the same files is there too.
Mac	MW3-Rebuild-<version>-mac.dmg	Drag the app to Applications.
Linux	MW3-Rebuild-<version>-x86_64.AppImage	Make it executable (chmod +x) and run it.

On a Mac, the first time: the app is not signed by Apple, so macOS stops it the first time you open it ("MechWarrior 3 Not Opened"; click Done, not Move to Trash).

• macOS 15 Sequoia and later: open System Settings > Privacy & Security, scroll down to the line about MechWarrior 3, click Open Anyway, then Open (and your password if asked). Right-click > Open no longer gets past it on these versions.
• macOS 12 to 14: right-click (or Control-click) the app, choose Open, then Open again. Open Anyway in Privacy & Security works there too.

macOS remembers your choice after that.

On Windows, SmartScreen may warn about an unknown publisher: click More info, then Run anyway.

The first start

Start MechWarrior 3 and it goes straight into the game when it finds your install: where the original installer put it, Program Files, C:\Games, a Wine, Proton or Lutris copy on Linux and the Mac, or a copy it installed itself earlier. It says which version it found in its log.

If it finds none, choosing MechWarrior 3 opens a screen that finds your game (a plain mw3 start shows only that screen), and once the game is there it goes straight on into it:

• Find the game searches this computer and your disc drives first and uses what it finds, with nothing to pick. If there is nothing, one picker opens: choose a disc image or download (an .iso, a .cue with its .bin files, whose CD audio becomes the music, or a .zip, .7z or .rar holding any of those, even a zip inside a zip; nothing needs unpacking by hand), or Mech3.exe (or any file) in an installed copy, which means that whole folder. It looks inside first and says what it found ("The MechWarrior 3 disc version 1.0, with its music (2 CD tracks)"), then copies what the game needs into a folder of the rebuild's own, with a progress bar and Cancel. An installed copy is used where it is. No Windows and no original installer needed. Versions 1.0 and 1.2 both work as they are: 1.0 plays as 1.2. Pirate's Moon is recognised, but its support comes later.

If something is wrong (not enough space, a damaged download, a file that is not MechWarrior 3) it says so in plain words and changes nothing.

• The launcher, installed as "MechWarrior 3" (the Start-menu and desktop shortcut on Windows, the Mac's "MechWarrior 3.app", the Linux desktop entry), is the rebuild's own front screen: the games. It starts the game and closes as soon as the game's first frame is on screen (if the game fails to start, it stays and says so). Game files there opens the same find-your-game screen at any time: to use another copy, install again from your disc, or add movies and music it lacks. mw3 (mw3.exe) also starts the game directly. The arrow keys and a gamepad work in the launcher as well as the mouse.
• Before the first game it tells you anything worth knowing about your copy: no movies (a CD-type install leaves them on the disc), no music, or game files of an unknown version. Add from my disc there takes what is missing from your disc in a drive, a disc image or the disc's folder.
• The movies play from your own copy. Where they cannot be played directly, the rebuild converts them once, the first time (about a minute).

Your MechWarrior 3 files are only ever read, never changed.

Music

The original played its music from the CD's audio tracks, which an installed copy does not have. Two ways to get it back:

• With a disc image (a .cue and its .bin): Add from my disc on the notes before your first game (installing from the .cue takes it at once).
• Your own rip: put the tracks in the rebuild's music folder (below) as track02.ogg, track03.ogg and so on (or .flac, .wav, .mp3), numbered as on the CD.

Playing

• The game runs fullscreen at your desktop's resolution, widescreen included. Alt+Enter switches between fullscreen and a window.
• In a window, press and release Ctrl+Alt to free the mouse; click in the window to take it back. Switching away frees it too, and coming back to a mission (Cmd+Tab, Alt+Tab or a click) takes it again at once; that click does not fire.
• Options > Graphics & Audio > Mouse sensitivity (ours) sets how fast the mouse aims in a mission; it starts at the original's setting.
• Gamepads work as they did on Windows 98, and force feedback becomes rumble.
• Flight sticks' axes (twist, throttle lever) go where the game expects them. With several devices, joystick=Part of its name in mw3.cfg picks one; an odd stick's axes can be set with joystick_axes=X,Y,Rz,S0 (one word a stick axis: X, Y, Z, Rx, Ry, Rz, S0, S1, or - for none). mw3.log lists every device found and the line in use.
• A stick's throttle lever covers reverse too: full reverse at the bottom, stop a little over a third of the way up. If yours runs backwards, untick Invert in Options, Controls, Assign Axis on Forward Throttle, and save when Accept asks. Toggle throttle direction (Backspace) is for the keys and does not flip a lever. throttle_reverse=0 in mw3.cfg gives the original's stop at the bottom (reverse is then Backspace).
• On a widescreen every screen uses the whole width: the missions, the menus, the mech lab, the briefings and the multiplayer screens. For the original's 4:3 menus, put widemenus=0 in mw3.cfg (or start with --no-wide-menus).
• The movies keep their shape on a wide screen: the intro and the ending, whose black bars were part of the picture, fill the screen's width; the 4:3 movies are centred with black sides.

Multiplayer

Multiplayer on the main menu plays the original's network games over the internet or a local network, up to 8 players. DirectPlay, which the original used, is gone from modern systems, so the rebuild has its own connection (UDP); IPX, modem and serial play are gone with it. Everyone plays the rebuild, on any mix of Windows, Mac and Linux.

• On a local network, games show up on the connection screen by themselves as soon as it opens.
• Joining by address: type the host's address (203.0.113.7, or 203.0.113.7:27930 for another port) and press Find Game or Enter.
• Hosting: Host Setup, then Host. The game opens its UDP port, 27930, on your router by UPnP when the router allows it, and closes it again when you stop. The connection screen and the lobby show the address to give your friends (click it to copy) and your LAN address. When the internet cannot reach you, the screen says why and what to do:
  • "forward UDP 27930 on your router to host": no router answered, so set up the port forward by hand in your router's settings;
  • "Could not open the port": the router refused UPnP; forward the port by hand;
  • "Another router stands in front of yours": a second router (often the provider's modem) sits between yours and the internet; forward UDP 27930 on that one too, or use a VPN such as Tailscale;
  • "Your internet provider blocks hosting": your provider shares one internet address between many customers (carrier-grade NAT), so no one can reach you from outside. Play on a LAN, or over a VPN such as Tailscale; joining other people's games still works.
• Leaving a match: Escape shows "Are you sure you want to quit?". With bug fixes on (below) the match goes on while it is up, so you can still move and fire; Y leaves for the main menu, N or Escape closes the box. The others see you leave at once. A match also keeps running when its window is in the background, so your 'Mech is never a frozen target.
• Mods must match: a player whose gameplay mods differ from the host's is told which mods each side uses.

Bug fixes, and playing exactly like the original

The rebuild fixes the original's bugs where the intent is clear: things that ran faster on a fast computer, the mobile field bases that would not come back, lancemates walking into walls, and more. Quirks that players know and plan around are kept. Every change is listed in plain words in CHANGES.md.

To play exactly as the original did, turn the fixes off: start with --original, or put the line bugfixes=0 in mw3.cfg (in the folder below). The changes the game needs to run on a modern computer stay on.

Cheat codes

The rebuild adds cheat codes (ours, not in the original) for the campaign, Instant Action and training; a network game refuses them. In a mission, press Shift+Enter (or Keypad * or Keypad −) to open a one-line box, type a code and press Enter; Esc closes it. The mission keeps running while you type. Capitals and extra spaces don't matter. A code lasts until the mission ends; the ones that switch something on switch it off when typed again. The message panel says what was turned on or off.

Code	What it does
black sheep wall	Every mech and vehicle on the radar, at any range
power overwhelming	Your mech takes no damage
operation cwal	Your weapons reload and your mech cools ten times as fast
food for thought	Maximum salvage: every chance in the salvage goes your way
there is no cow level	Wins the mission: every enemy mech and vehicle destroyed by you and salvaged whole, every objective done
game over man	Loses the mission

A mission won with a code counts as won. In a network game the keypad keys stay the chat's. More in docs/cheats.md.

Mods

The rebuild loads mods: folders of game data in a mods folder inside the settings folder (below), laid out like the game's own files, each with a short mod.txt. A mod can change textures, sounds, text, missions and the game's data files, or add new worlds and maps; it never touches your install or your pilots. List them in mw3.cfg (mod=NAME, one a line) to turn them on; mw3 --mods lists what it found, and mw3 --check-mod FOLDER reads a mod as the game would and says what it would refuse. With no mods turned on, nothing changes. How to make one: docs/modding.md.

The original game has a tool of its own here: tools/weapon-patch adds weapons to the original Mech3.exe's mech lab. It isn't part of the rebuild.

Where your saves and settings go

	Folder
Windows	%APPDATA%\MicroProse\MechWarrior 3\
Mac	~/Library/Application Support/MicroProse/MechWarrior 3/
Linux	~/.local/share/MicroProse/MechWarrior 3/

It holds mw3.cfg, your pilots and saves, the settings, the converted movies and the music, and mw3.log. Uninstalling the rebuild keeps it; deleting it starts you over.

Known issues

• macOS: window tools can delay the mouse button by about a second. Tools that filter mouse clicks to snap or move windows (Magnet and similar) can hold each mouse-button press back, so in a mission the mouse fires only when you let go. The keyboard is not affected. Quit the tool while you play, or add MechWarrior 3 to its excluded apps if it has that setting.

Reporting a bug

Open an issue and include:

• what you did and what happened (a screenshot helps);
• the mission, and whether it happens with --original too;
• your system (Windows, Mac or Linux, and the version);
• mw3.log from the folder above. It is written new at every start and the one before is kept as mw3.old.log, so if you started the game again after a crash, send mw3.old.log.

Hidden mechanics

Taking the game apart turned up hundreds of hidden mechanics, quirks and bugs, collected for players in docs/discoveries.md. A few:

• Lasers never cause critical hits, and criticals only happen once a part's armor is down to 15%.
• Ammo criticals don't explode: they just empty a bin. CASE in a side torso does nothing at all, and the stock Mad Cat carries both of its CASE there.
• Ultra autocannons never jam; they simply fire twice as fast.
• TAG works, but the missiles home on the spot you marked, not the target, and take 7 seconds to arrive.
• Pilot files track hidden Instant Action and multiplayer stats that the game never shows.

For the curious: start with --debug-camera (or put debugcamera=1 in mw3.cfg) and press Shift+F12 in a mission to open the game editor the original carries but never lets you reach: its menu over the mission, and the view on the invisible "stealth" camera, flown with the movement keys. Shift+F12 again puts the view back on your 'Mech. It is a developer's tool, as it was in 1999: expect rough edges.

Building from source

See docs/building.md. How the code is organised (the shared engine, MechWarrior 3, Pirate's Moon and the launcher): docs/games-layout.md.

Credits and licence

• MechWarrior 3 was made by Zipper Interactive and published by MicroProse in 1999. All the game's content is theirs and comes from your own copy.
• The rebuild is by Owen Morgan, under the MIT licence. The original's code was studied with Ghidra and REA, the data formats cross-checked with mech3ax, and the port checked against the original in the Unicorn emulator.
• It runs on SDL3 (with SDL3_ttf, FreeType and SDL3_sound), and converts the movies with a minimal LGPL build of FFmpeg. Each download lists them in `THIRD-PARTY.