A long time ago i ran a Ct Campaign that had a 400 ton adventurers ship that visited the D&D world that has Greyhawk on it .
I think its Oerth (Not Sure Though )
They had an armoured ATV .
They landed near the Evil Necromancers Castle(They just thought it was a low tech fortification) and
were promptly attacked that evening by Said Evil Necromancer who did not like big metal buildings that appeared suddenly on his land.
They used heat seeking ram grenades and other heat seeking weapons as well as almost every weapon in CT (Typical Adventurers Armed to fight D Day By Themselves)to cream the attacking humans, but later on in the night they were attacked by beings with no IR signature and all the IR devices could not see them and the heat seeking munitions missed and ditto for the Automatic activating weapons.
The beings were Skeletons ,Wraiths,Spectres,Zombies,and the vampire that charmed the Marine in the powered armor who protected the Vampire from the party.
The Zombies took almost no damage from Fire arms .
The Spectres and Wraiths only took damage from lasers and the vampire only took temporary damage from all but Hvy Lasers .
In the morning the party used the ATV and
promptly fell in a pit dug with the dig spell and covered by an illusion .
He sent in his Red Dragon to roast the ATV.
The VRF Gauss Cannon on the ATV hurt the Dragon a lot and it flew away to lick its wounds .
Then the Necros Druid Follower used heat metal and fused the ATVs hatches and turret shut and immovable so the party members couldnt get out.
Then his incorporeal undead arrived and could walk through the ATVs walls and Attack .
It was an interesting and scary fight for the party.
They found using grenades and auto or fast firing laser weapons and auto fire of any kind inside a vehicle is a Very Bad Idea.(Lots of collateral damage)
Unfortunately for The Necro the sun came up and the powerful undead fled .
Then the crew that had been in the ship used the laser turrets to cut the Necros tower into little bitty pieces and then rescued the crew from the ATV
Then in broad daylight the party looted the remains of one Very Pissed off Necro's Castle .
This campaign went on for a while ,the way i described things worked so that even though we all were expert D&D players they did not guess it was D&d for a while .
They thought it was Very High Tech world Or VHTW combined With PSI Powers on a world that only appeared to be Low tech Feudal .
I had gotten the idea From a Miniature/RPG Game called Space Marines and some ideas from the Strategic Review (The predecessor of the Dragon )article on the Nazi Armoured column that somehow was transported to Oerth via a Summon Spell + wish .
I think at this time the Dragon article on the Traveller in D&D adventure wasn't out yet,But it is a good Traveller to D&D Conversion Idea as i remember .
For help on Sci Fi to D&D the AD&D Dungeon Masters guide has a good section near the back which includes conversion of boot hill to D&D which i had fun running too.
I remember Deputy sheriff Jim pulling his metal hatchet and killing the 5 orcs who thought he was dead meat (Metal hatchet= holstered six gun with Fast draw and Dead Shot skill + very high Dex)
And the fun he had when he was attacked by the archers and used his Winchester 76 Rifle from the ground which the archers thought was unfair as they died standing and loosing arrows .
Deputy Jim was in a campaign I played in 25 years or so ago .
Here are some of my conversions that i used .
Normal firearms are non magical arrows so no damage to Skeletons and 1/2 damage to Zombies,
Portable Laser weapons counted as +1 Magic for Spectres and Wraiths and Vampires .
Normal Explosive Ram Grenades counted as non magic
Incendiary Grenades of all types counted as Magical Fire and did X2 damage to Zombies and creatures vulnerable to fire .
The VRF Gauss Cannon counted as +1 Magic on all but Incorporeal Undead .
The Ships weapons Counted as +4 or +5 Magic AOE depending on the creature .
The crew basically started as 1st level and depending on what they did in game became either Fighter,Cleric,Mage,or Thief
As an example,
The ships medic became a 1st level cleric with no spell ability until he started investigating the Prayer books they found in the ruins .
The Army or Marine types were 1st level Fighters who got fighter abilities as they fought creatures and learned new methods of fighting .
The Character who got curious about the strange books on PSI powers (As he thought magic was )became a 1st Level Mage with no spells .
When they started they had basic 0 level saves versus spells
I never said when or if they gained levels .
I kept track of exp and level gains and powers and when it happened i would tell the cleric after weeks of study, you feel you can try the PSI Power of healing,to the mage you have learned the secret of the Psi Energy Bolt( Magic Missile)
To the fighter you have learned to swing your sword to hit more often .
The recon man you have learned how to move to lessen the chance of being heard or seen as you move.
Hope this helps a little on ideas for you
If not well i had fun rembering past Traveller games
Maybe some day i will tell the story of the 3 adventurers in powered armor with grav belts armed to the teeth with every weapon they could carry + a small mantowed grav cart for ammo and more weapons and the recon scout in light kevlar vest and carrying a 45 Auto only.(He was the only one to walk out and not be carried out feet first )