Increasing levels of Russian submarine activity in the North Atlantic and a steady stream of their vessels passing the UK is the new norm, the head of the Royal Navy has said.
First Sea Lord, Admiral Sir Philip Jones, offered insight into current threats and what the future holds for the Royal Navy and Royal Marines.
His statements came as he delivered the Gallipoli Memorial lecture at the Royal United Services Institute on Thursday.
He warned that today's Armed Forces "must work in an increasingly complex battlespace".
He added that the "degree of superiority at sea" which Western navies previously enjoyed post-Cold War is diminishing, as the space they operate in becomes more congested.
"You don't need to look very far to see rising and resurgent powers flex their muscles," he said.
"It's now clear that the peaks of Russian submarine activity that we've seen in the North Atlantic in recent years are the new norm.
"The same is true of the steady stream of vessels passing the UK on their way to join the Baltic, Mediterranean and Black Sea Fleets."
He said there are currently almost 500 submarines being operated in the world's oceans by more than 40 navies.
And also warned how sea mines, "which remain, cheap, easy-to-use and plentiful", present an issue and stockpiles of these held by North Korea and Iran are estimated to be in the thousands.
The head of the Royal Navy highlighted how China's navy now sustains routine deployments to the Middle East, the Somali Basin and the Gulf of Guinea.
"Earlier this year we saw a joint Russian-Chinese naval exercise in the Baltic. Suddenly, our own European backyard is a little more crowded," he said.
"Our response cannot simply be to avoid operating in these environments; we don't have that luxury."
"Areas of enclosed water, like the Baltic and the Persian Gulf, are essential to global security today, and will remain so."
With the commissioning into the Royal Navy of HMS Queen Elizabeth just two weeks away, he said:
"I have every expectation that the pairing of the Queen Elizabeth-class carriers with their fifth generation F35B Joint Strike Fighters will quickly become a valued asset, in constant national and coalition demand."
He said the F35B jet represents a "quantum leap" over anything the Navy has operated at sea before, and combines speed and manoeuvrability with the advantages of stealth, electronic attack and sensor fusion.
As part of a national security review, cost-cutting suggestions ahead of any formal announcement, have reportedly included the axeing of amphibious assault ships HMS Albion and HMS Bulwark.
There is also talk of axeing 1,000 Royal Marines.
The First Sea Lord said the Royal Marines are an "inseparable part of the Royal Navy" and as head of the service he will "fight for them every step of the way".
He stressed the Royal Marines have "rarely been more relevant to the threats we face", but said as the service looks forward to a "carrier-centric future" they must adapt, as they have done before. He added:
"However, I want to be clear that this does not mean our investment in Carrier Strike comes at the expense of the Royal Marines."