Classic Traveller has two major editions: "CT-77" and "CT-81".
The pre-81 vs post 81 changes are pretty impressive:
- change of damages from Xd+Y to Xd
- Surprise DM's (more in 2E)
- Encounter distance table has more terrain types on the DM's table.
- Combat movement handled slightly differently.
- Changes in ship design requirements
- in 1E, PP≥MD, in 2e PP≥max(MD, JD))
- In 1E, computer must be able to run the correct jump prorgam, in 2E, it must have a model number at least equal the Jn.
- Changes in the drive performance table
- Changes in standard hull construction times (2E less across the board)
- changes in nature of space encounter tables
- Changes in ship combat scale (1E: 1"=1000mi, 10 minute turns; 2E: 1cm = 1000km, 1000s)
Noting the performance differences in the Bk2 drive tables:
Tonnage | Drives | 1E | 2E |
3000 | Y | 3 | 2 |
2000 | J
Z | –
5 | 1
6 |
1000 | E,F,G
W
X
Y | –
4
4
5 | 1
5
6
6 |
800 | DE
XY | –
5 | 1
6 |
600 | C | — | 1 |
400 | B | — | 1 |
MGT has a different table still, just for reference.
There are some further fairly minor changes from the 81 edition in the Traveller Book and Starter Traveller.