What Happened to the Sub in "Fantastic Voyage?"

It is a problem, because it is not made entirely clear how the process is achieved. The sub would have lost some molecules of itself as it travelled through the body. The people - even in their suits - would have lost pieces of themselves. These clearly did not expand back at the end if the time.

A suggestion - maybe the re-expansion required a certain level of integrity with the original before it would work. In other words, the people were substantially the same as the people who went in, and so the re-expansion was smooth. The ship - and Dr Michaels - had been sufficiently compromised by the attach of the white blood cell that they were no longer integral enough to expand. Over time the molecules passed out of the system.

This is also full of holes I realise, but it might serve as a start.

I believe the white blood cells engulfed the digestible parts of the sub - the minerals, the iron, etc. Whatever was left would have most likely fallen apart even if it DID expand, without enough molecular bonds remaining to hold it together. If the sub's remains were in a major artery within the brain, they could have been carried away by the blood flow. If this were the case, the remains would have been further crushed by that same blood flow, like a rickety raft in fast flowing rapids. Eventually, the remains would be so small, even compared to before, that the white blood cells would have taken care of whatever was left.

Consider also the volume of miniaturized water injected along with the ship. It too would expand and 'pop' the good doctor from the inside. Water would not be recognized by the body as foreign.

The ship would have had to have been removed along with the crew as the body cannot break down even normal sized pieces of shrapnel from war wounds even after years.

Still, an excellently shot, beautifully done movie. The only PG movie where Raquel Welsh is groped by three men.

IIRC, in the novelization, Asimov stated the miniaturization process could also be done in reverse, enlarging things (I recall a line about sizing an ant up to that of an elephant for study). It was casually mentioned that the syringe and the water/solution inside it were enlarged from normal (descriptions of the difference of water ripples due to size were in there too) to "meet the sub half way" in size. Thus the apparent "gallons" in the syringe were actually only several milliliters worth in volume.

In addition, Asimov mentioned that the "light" of the miniaturizer was extra/super-dimensional radiation which the eye/mind only interpreted as light. Invoking extra/super-dimensional physics leaves plenty of technobabble "wiggle room" regarding minor things not properly addressed.

Pretty much it gets dissolved in the novel. The movie suggests,it get dissolved inside the brain of Benish. I guess, because it partially exists in hyperspace,while tiny,it get trapped there,too.

Asimov accounted for that in the novel by getting the white cell to follow them to the eye and be removed with the Team. However, the movie ignored that issue. The water in the syringe was prepared prior to final miniaturization, so it could remain in the patient without harm.