More than 150,000 anti-radiation pills are being stored in schools and colleges following the arrival of a nuclear-powered submarine in Portsmouth.
HMS Torbay is in Portsmouth until Saturday
The potassium iodate tablets - designed to stop radiation from reaching the thyroid gland - have been issued as a precaution during the visit by HMS Torbay this week.
Stockpiles, which are normally held centrally, have been handed out in a two-kilometere zone around the naval base.
The area's emergency planners have reassured residents that the chances of a radiation leak are extremely unlikely.
Alasdair Hogg, Portsmouth's emergency planning manager, said: "Every practical step has been taken to ensure their safety and we reassure them now that there shouldn't be any problems whatsoever."
The pills have been stockpiled in schools and colleges
HMS Torbay, a Trafalgar-class submarine, which has come to the city's dock for a round of official visits by senior officers, is due to leave on Saturday.
The Royal Navy says the type of precautions being taken are common place in Plymouth where the submarine is normally based.