Yes, we need a standing Navy for a number of reasons:
1) It is Our First Line of defense for any attempt any invasion.
2) It secures our shipping lanes.
3) It provides a "well" of military experience which can be drawn upon.
What we don't need is a standing Army which is why the founding fathers limited authorizations for the US Army to two years at a time.
The following is an addition (slightly off topic but applicable) resulting from a discussion in comments:
Here's why I make these assertions: Johnson handed Nixon had a perfectly good plan to end the Vietnam War. Nixon scuttled it until the whole nation rose up and demanded an end to the war.
Cui Bono? (Who profited from this):
It wasn't the Citizens who got stuck with the bills for the war.
It wasn't the nation which took a huge hit in perception because of the war.
It wasn't the Constitution.
so who profited?
We've been in a nearly continuious state of "police actions" (Aka war, under a new less henious, Orwellian name) ever since.
Now, since we've never been invaded, and the Army is specifically prohibited by Our Constitution from operating within the nation, except under vertical limited circumstances; where is the valid logical argument for a large military? Especially considering the words of Hirohito, when he was asked why they (one of the most warlike, effective, nations we had ever faced in theatre) didn't invade the US… "There is a gun behind every blade of grass."
This takes us right back to the same old Question: Cui Bono?!
Bottom line: There is zero Constitutionally, nationally, or logically, valid reason for maintaining a massive Army (which causes us to spend more than the next 14 "big spenders combined when 1/5 that cost would protect us very nicely) unless you take a long hard look at who profits from this standing Army (which was strictly limited by the Constitution to two years and then everyone but a few officers goes home).
So… Cui Bono?
Halliburton (Cheney and Bush owned) … +$39 Billion that we know about of which hundreds of millions *Poof* *vanished* due to "accounting errors."
Xe. (Or whatever they're calling themselves now in order to evade legitimate prosecution for their war crimes and murders)
Other Mercenaries (conveniently called "security forces" by our Orwellian government)
Wall Street (Despite their very loud assertions they absolutely adore "uncertainty"… so long as they can plan for it)
K Street (funneling "contributions" to politicians for over 50 years)
And these guys… some of the most "generous" bribers of Our Congress:
These are the only folks who profit from wars.
Everyone else… US Citizens, the Nation, Our Constitution, the so called "enemy"(entirely created by US Top Secret meddling), gets completely and utterly screwed (without the benefits of a kiss or butter).
I see good valid reasons for keeping a few thousand officers trained and ready, I don't see any legal, or valid reason for hundreds of thousands of soldiers to be "Standing by" "just in case" for an event which has never happened, and is extremely unlikely to happen for several reasons.
1) There really is a gun behind every blade of grass from any invaders' perspective.
2) Whatever our differences Americans pull together when attacked… that's a truly frightening prospect to anyone considering such a foolish action, and everyone knows it.
3) Supply line logistics are completely horrendous.
4) Consider what would happen were an army actually to attempt to land on our shores! Let's say 10,000 or so… Every single "gun nut" in the nation (hundreds of thousands easily) would be on site in days. Many, many of those folks have military experience.
5) The only practical way would be N.B.C. weapons which would trigger mutually assured destruction… Game Over.
So where is the logical justification for a large standing Army if we remove corporate profits of Congressional Bribers from the equation?
There isn't one.