Duffy (Lieutenant junior grade)
Lieutenant junior grade Duffy was a male Human Starfleet officer in the 24th century. He became an engineering technician stationed on board the  in 2366. 

During 2366, Duffy assisted with transporting tissue samples from the Mikulaks into cargo bay 5 along with Miles O'Brien. Unfortunately, he was accidentally contaminated with invidium and subsequently spread this element throughout several ship's systems. During the trip, he was assigned to realign the magnetic capacitors in the matter/antimatter injectors, together with his colleague Costa. 

While drinking a beer in Ten Forward, he contaminated his glass with the invidium and thereby changed its molecular structure, causing it to leak. After discussion with the senior engineering officers, he realized what happened to him. He underwent bio-decontamination on Starbase 121 with several other officers. ()

Background information 
Duffy was played by actor Charley Lang.

Duffy was referenced in a deleted scene from  when Geordi La Forge told another engineer that Duffy was to adjust the main deflector and look into an inducer problem.

Apocrypha 
In Pocket Books Star Trek: Starfleet Corps of Engineers series, Duffy appears (in the post-Dominion War era) as the second officer of the series' ship, USS da Vinci, rank of lieutenant commander. In the books, his first name is Kieran, which coincidentally is also MacDuff's first name. He is also said have had a past relationship with da Vinci first officer Sonya Gomez when they both served aboard the Enterprise. When the da Vinci became trapped in the atmosphere of the gas giant Galvan IV, Duffy gave his life to complete his mission and ensure the safety of his crewmates.

External links 
 
 

de:Duffy (Lieutenant Junior Grade)
Humans
Starfleet operations personnel
USS Enterprise (NCC-1701-D) personnel
Deleted and unused material in background