No, but for a short while in 1989 they were the owners of 17 ex-military submarines.
In 2000 China had about 65 submarines.
In 1990 Britain had about 29 submarines (about ten now).
Currently Japan has the sixth largest fleet of submarines with seventeen submarines.
So it is plausible that in 1989 PepsiCo briefly owned the sixth largest "fleet" of military submarines - though it seems certain they were demilitarised. It seems likely they were not in usable condition and were towed by surface tugs to a scrapyard which could pay in US dollars. So the assertion is somewhat poetic rather than factual.
New York Times, 1989: Soviets Buy American
Pepsico recently bought from the Soviets 17 submarines (for a measly $150,000 each), a cruiser, a frigate and a destroyer. They are being resold for scrap.
These peculiar ventures for a soft drink company are a necessary way for it to do business with Moscow. Pepsi has 21 plants in the Soviet Union and wants to open 26 more. The problem, as in most deals with the Soviets, is how to get the money out.
So really it has more to do with the problems of converting currency of the the Soviet Union into hard currency, not to do with PepsiCo's naval ambitions!