HMS Queen Elizabeth sails alongside two Royal Navy frigates (Picture: MOD).
The size of the Royal Navy fleet is "pathetic", according to the chairman of the Defence Select Committee.
In an interview with Sky News, Dr Julian Lewis MP said: "All the Armed Forces are under-resourced financially.
"That means we're incapable of putting together a range of options to defend ourselves, which is fine as long as there is no threat and is potentially disastrous if a conflict arises as most conflicts do - unexpectedly and unpredictably."
His comments come after the UK announced extra ships would be sent to the Gulf in response to growing tensions with Iran.
Type 45 Destroyer HMS Duncan is currently sailing to the region to fill in for HMS Montrose when she docks for maintenance.
Meanwhile, two additional ships, HMS Kent, which will take-over from HMS Duncan, and RFA Wave Knight will also be deploying to the region later this summer.
Type 23 frigate HMS Montrose is currently the only Royal Navy warship escorting British-flagged ships through the Strait of Hormuz.
Dr Lewis said he is concerned the Royal Navy does not have enough warships as it waits for its two aircraft carriers to become operational.
"In order to allow for the carriers being provided for, it was agreed that we would reduce our frigates and destroyers from 35 ships to 32," he said.
"It was never envisaged at the time of the aircraft carriers being conceived of, that we would go down to the present pathetic total of 13 frigates and six destroyers.
"What Boris Johnson needs to do is to recognise that if defence is the first duty of government then we've got to get back to the levels not that we spent in the 1980s, but the levels that we spent as a proportionate of GDP in the 1990s."
Earlier this week, Dr Lewis questioned the new Prime Minister on what he is going to do with the Royal Navy.
"Does he [Boris Johnson] accept that events in the Gulf have cruelly illustrated the fact that the size of the Royal Navy is now way below critical mass?," Dr Lewis said.
"So, will he join with the Defence Committee in wishing to reverse the reckless reduction in defence spending by successive governments?"
Mr Johnson replied: "I share with him a strong desire to increase spending, in particular on shipbuilding."
Rear Admiral Chris Parry, a former commander of the UK's amphibious task force, also told Sky News: "90% of all our trade goes via sea, so those things that go virtually on the internet, actually go really by sea.
"So, it is totally irresponsible for any government not to invest in sea power."
A Ministry of Defence spokesperson said: “The Royal Navy plays a pivotal role in maintaining freedom of navigation around the world.
"In recent weeks, our presence in the Gulf has deterred attacks and protected over 30 merchant ships as they pass through the Straits, ensuring the free flow of trade.
“We will continue to work with our partners and allies to maintain this truly global presence, while heavily investing in new capabilities such as our two new aircraft carriers and Dreadnought submarine programme.”