A nuclear attack submarine carrying a crew of, at least, a hundred people went missing in the North Atlantic Ocean, its last known location was the Bermuda Triangle where ships and planes have vanished. Cutting to the chase; the sub has traveled back in time several hundreds of millions of years into the Jurassic period. How likely is it for the crew to survive a whole year in the Jurassic sea and maybe surface once in a while for a cigarette break? Assuming it was on its maiden voyage in crossing the Atlantic Ocean when it mysteriously got lost inside the Davy Jones's locker.
In addition to the food mentioned by James K, spares will become a problem sooner or later. Parts wear out. They are supposed to be replaced before they break. The sub has an engineering crew which can probably jury-rigg some parts, but not everything.
The US Navy uses submarine tenders to maintain subs at remote locations. Look at the crew numbers -- ten times as many as a submarine. Quite a lot of them are maintenance specialists.
The problem the crew will face is that during the Jurassic period the CO2 level of the atmosphere is 5-10 times higher (2000 - 4000 ppm) than the current level (400 ppm) and the oxygen content was on an all-time low of 15% in the beginning which rised to 26% at the end of the Jurassic (in comparison to 21% now):
Graphic from author Robert Rohde from the Global Warming Art project licensed under CC BY-SA 3.0
The interesting things are the blue line and the points with crosses which are actual measurements. While it looks not so bad at first, there is evidence for very high levels (2000 - 4000 ppm).
The run-away greenhouse effect caused global warming at a level which is hard to imagine now. Nearly everywhere the climate is tropical, extremely hot (40°C+) and very hard to cope with. In the Jurassic era the continents begin to split up to form our modern ones, the Atlantic ocean is only looking like a big saltwater lake.
The sea level is much, much higher than now (missing ice), so navigation are mostly useless (What does work is the gyrocompass, echo sounding and astronomic navigation). The ocean is nearly everywhere over 25° warm, up to 30°C at the equator and 19°C at the poles, so expect terrible hurricanes forming at the coast.
Some hints apart from the climate and the occasional plesiosaur sticking out the head of the water that they are not in Kansas anymore:
The day lasts only approximately 23 hours (tidal slowdown).
The moon is looking bigger (It is nearer to Earth).
The magnetic compass shows in the completely wrong direction (the magnetic pole is wandering and sometimes even reversing direction).
The sky looks foreign. The sun revolves the galaxy once in 220 million years, so the Earth is in the wrong position. It is still possible to use astronomical navigation for several purposes, but the crew must prepare their own observations.
Light sensors show that the sun radiation is slightly reduced by 3%.
The submarine has fortunately CO2 removers, air conditioning and could produce oxygen with electrolysis, so it may be comfortable, but they may want enter land sooner or later.
The effect of 2000-4000 ppm carbon dioxide and low oxygen content is that the air feels suffocatingly bad, you get headaches, are lethargic and feel like drunk.. While the article on carbon dioxide poisoning claims that human can adjust to levels up to 10 000 ppm permanently, the time will be unpleasant (In this case don't forget that if they come back the air smells fantastic).
Anyway, your crew will suffer. High temperatures together with high humidity and bad air will cause very high stress levels.
Food is the limiting factor.
The nuclear motor can operate for 25 years, and it has desalinators, active CO2 scrubbers and oxygenators to provide air and water for the crew for as long as it has power.
This article, which concerns the British Sub, Artful, notes that a normal deployment lasts 10 weeks, and a sub won't carry enough food for a year. It would be possible for the crew to survive on short rations for a while, but a full year is probably too long for the whole crew to survive without finding another source of food.
The natural place to find food would be fishing. Fortunately Wikipedia has a category on Jurassic fish.