"My guess is that the US and Brits know exactly where their subs are at all times." - Toad The Persian gulf is noisy, littoral, and known for it's temperature and salinity gradients. All things which strongly favor the Kilo boats as opposed to US nuclear submarines which were designed for blue water operations. The US has allowed it's ASW capabilities to atrophy following the end of the cold war. I would not count on the Kilo being detected.
Ofir Akunis officially replaces Danny Danon as minister of science, technology, and space (Haaretz)
from the article: Iran Revolutionary Guards: Unit engraved emblem on U.S. ship