Supplement 4 is part of the german Traveller Rulebook II ( it included following: Book 4 -
Mercenary, Book 5 - High Guard, Book 6 - Scouts, Book 7 - Merchant Prince, Supplement 4 - Citizens of the Imperium, Supplement 12 - Forms & Charts, Special Supplement 2 - Exotic Atmospheres, Special Supplement 3 - Missiles, as well as some additional material from Supplement 7 - Traders & Gunboats, Game 3 - Azhanti High Lightning, Adventure 1 - The Kinunir, Adventure 5 - Trillion Credit Squadron, JTAS 17 - Air Strike, JTAS 20 - Temperature and Challenge 26 - Cargo).
And missing is the armor/range table for the archaic missile weapons. They are even missing for the rules from Game 3 - Azhanti High Lightning (but thy were include in the so called "Action Pack" which featured the combat rules from Game 3 - Azhanti High Lightning with counters deck plans and 2d6.