Speaking very broadly there are two types of light expeditionary forces:
1. Air mobile (may be some form or combination of air lifted, airborne, air assault ... I am no longer sure of the correct phraseology); and
2. Amphibious.
The differences are more than just skin deep.
Air mobile forces can deploy (in relatively small numbers - say a light infantry battle group) quite quickly. An 'air bridge' can be established in a few days, and then, depending upon the distance from the local (tactical) airhead to the objective or area of operations, somewhere between 10 and 30 serviceable Hercules type aircraft can do the job, but 'sustainment' becomes a problem and, until a 'land bridge' is established, getting adequate heavy equipment is a bigger problem - even a troop of Strykers consumes lots of air lift.
Amphibious forces are slower to deploy - 20 knots, tops, I guess - but once "on station,â ? in an area they can linger and lurk until needed, often for protracted periods. This makes them especially useful when one wants to practice gunboat diplomacy which, over the centuries, has proven to be very, very effective. I suppose amphibious force can be mechanized, and the USMC have (lightly) armoured amphibious vehicles and main battle tanks, etc, but they are, I think, lighter than a conventional, general purpose mechanized battle group which the Canadian Army favoured a few years ago - although heavier, usually, than their air mobile confreres. Amphibious forces can also be deployed and then sustained for protracted periods from the landing/assault ships - over the beach, if necessary but, preferably, through a local, captured or controlled seaport which makes offloading quicker.
Having one or more of either or both types of expeditionary forces requires:
"¢ Continued transformation in the army, I think, but I will let people like pbi, PPCLI Guy, 2Bravo and others guide me on that; and
"¢ Investment - heavy investment - in the Navy and Air Force to procure and sustain strategic amphibious/assault shipping (and protection/escorts for these valuable assets) and strategic and tactical air lift.
I think some of that may be in the current, approved defence programme (factored in to previous budgets) but the 'new' $12.7 Billion can be consumed pretty quickly when buying ships and aircraft.