UPDATE 5 March 2014: The nuclear warfare message from Russia last night was clear as a bell. It is a message that Vladimir Putin delivered with the launch of a Cold War era, road mobile RT-2PM 'Topol' (NATO Name: SS-25 'Sickle') ICBM. This ICBM is normally armed with a single 550kT nuclear warhead and multiple decoy warheads. Russian Strategic Rocket Forces launched the SS-25 (image below) from their Kapustin Yar site on the Volga River, some 280 miles east of the Ukrainian border, towards a target that was successfully impacted 1,230 miles distant at the Saryshaghan range in eastern Kazakhstan. On a reciprocal bearing this SS-25 would have made impact in the heart of Poland or one of the other newer member NATO nations in Eastern Europe. The message from Putin to the West: Is Ukraine worth fighting a nuclear war over?
4 March 2014: For their part the Ukrainian military is doing more than just calling up a million men from their reserve forces. Reports have come in of on-the-move Ukrainian armor. Whether they are the brand new Ukrainian-made BMP-64 Infantry Fighting Vehicles or older BMP-2 versions is unclear, but they are definitely enroute to a deployment in the south of the country. Other Ukrainian BMP-2 armor and troops have been noted maneuvering to fighting positions within their garrison at Perevalnoye. This garrison is currently surrounded by Russian special forces troops from the initial invasion last weekend. There were also Ukrainian Sukhoi-27 (Su-27, NATO-Name "Flanker") flying heavily-armed combat air patrol (CAP) missions out of their base at Mirgorod. Below is an image of an Ukrainian Su-27, callsign "45 Blue," as it went wheels-up on a CAP mission two days ago from Mirgorod. The heavy weapons loadout on "45 Blue" consists of a total of 10 air-to-air missiles, five each of the Vympel R-27 long-range, and Vympel R-73 short range IR homing air-to-air missiles, plus the internal 30mm cannon which always means nasty business.
For what its worth, IF, and as you can see that's a very big IF, there were to be a show of American military support it would come in the form of the USS George H.W. Bush (CVN-77) which is now in the Mediterranean Sea with her Carrier Strike Group (CSG-2). Also in the Med are the Marines of the 22nd MEU embarked on the USS Bataan (LHD-5) and ESG-2. There are also the Army 173rd Airborne Brigade at Vicenza, Italy and at least one battalion of the 82nd Airborne Division which is on-call to deploy anywhere in the world on very short notice. These forces would constitute a trip wire that could conceivably bring the entire U.S. arsenal to bear if full-scale warfare were to erupt over Ukraine. In any eventuality these are the US forces that would be the first on the scene if the currently unthinkable became a reality in the short term.