What's the most lethal vessel in the Navy's modern arsenal?

A carrier battle group, has more fire power than a lot of countries whole military. But that would include a Carrier, a Cruiser, a few Destroyers, and at least one Attack Sub in the fire power. For a ground campaign, An Amphibious Read Group is a lot of fire power too, 4 plus thousand Marines, and aircraft from an LHD/LHA, and after I left the Amphib Navy I understand they normally have a DDG in the ARG now.

Carrier.

I'm partial, but any amphibious class, LPD, LHA, etc. Destroyers are perimeter defense with impressive, but limited strike capability...carriers really should be classified "mobile installations"...subs are elite in their own right without comparison...but only the "Gators" take Marines to the fight and keep them there ;)

Submarine

Being on the old Spruance Class Destroyers, I want to say them because we could take out all the other ships and submarines and still have plenty of firepower to level the whole coast of California. However, after doing plenty of plane guard duty next to numerous Aircraft Carriers, I have to concede to their power. I also thought we were the fastest ships in the fleet because we had 4 LM 2500 gas turbine engines as well till I saw the USS Constellation CV-64 pass us by in a long haul race as if we were a snail. And to think, she was powered with conventional steam powered boiler engines to make it worse on us. I tip my hat off to her.

With today's technology all surface craft without superiority intercept capabilities are vulnerable to attack. The advanced technology would all aspects of battle. With the days small military we must be much stronger technically in order to beat any challenges our Navy today is overstressed and the same size we were in 1915. The other on services are too below prior war war 2 defensive posture. Your Air force was established in 1947 and today even that is considerably smaller. We're too small at this time today under the Constitution's top priority to protect safty and defend our nation. A small armed forces means less strength in numbers as well as armormen's as well as training capabilities for reliable replacements. Now we can't even maintain a carrier strike force to offset Iran's movements and requested that the French cover for us with their carrier. Once we can't control sea lanes a major source of logistics supply, we are again vulnerable to losses both at sea and land forces. Yes, at this time a carrier strike force is an asset, but with an 11 carrier inventory isn't capable to respond quickly enough. Our next conflict won't give us the time we had before WWII. With shipbuilding able to turn out ships and tanks like an assembly line production or years to train and increase our military. We will have to fight with our present capabilities and hope for the best. It just may be on our shores with allies also weak in their defense postures too.

SSBN

Lethal how?
The nuclear subs are still best, so far.

Carrier... Its ability to transport and deploy multiple weapons systems is unparalleled.

Hands down in today's environment it is the Carrier