Russia Won't Start a War With Ukraine Out of the Blue.

Russia's military buildup in Eastern Europe has led many governments, including the U.S., to believe that some form of attack against Ukraine is imminent.

A major war—which experts warn could be the largest conflict in Europe in nearly 80 years—would not likely start at a moment's notice. Instead, the Kremlin would complete preparations from behind a shield of cyber warfare and electronic jamming, while deploying drones and "little green men" events that would provide some warning signals to the world.So far, Russia has amassed more than 100,000 troops in Russia, Belarus, and Russian-occupied Ukraine, with more troops streaming in by the day.

The Russian Army Ground Forces have deployed elements of ten armies and army corps in the vicinity of Ukraine, amounting to several thousand tanks and infantry fighting vehicles and hundreds of artillery pieces, helicopters, and air defense systems. Moscow has deployed forces from as far away as Vladivostok (4,000 miles away) and invested so much effort in the operation that it seems unlikely this force has been amassed for a simple show of force.

No one but Russian President Vladimir Putin knows what he intends for Ukraine, but things aren't looking good for Kyiv. If war does come, there will be signs in the weeks and days beforehand that hint not only at its approach, but the size and nature of the conflict. Here are some signs to keep an eye out for, starting two weeks before the onset of war.

Fuel and Ammunition Stockpiles.

The Russian Army's massive deployment on the Ukrainian border has mostly consisted of military hardware, with videos of tanks, infantry fighting vehicles, and even long-range surface-to-air missile systems showing up on social media. But in order to actually wage war, Russia will need to stockpile vast amounts of diesel and aviation fuel, as well as ammunition; these war stocks have yet to be pre-positioned near the Ukrainian border. Additionally, Russia has not yet established field hospitals in-theater. If the videos shift from main battle tanks to fuel storage trucks and rows of rubber fuel bladders sitting in fields, it will mean Putin is not just showing off his Army—he intends to use it.

Cyber Warfare.

Modern warfare includes not only traditional kinetic means, but also cyber warfare. Russian military hackers can be expected to fully target Ukraine's computer networks, particularly those owned by the national government, utilities, financial institutions, and emergency services. Ukrainians could find themselves locked out of their bank accounts, the power might fail in the middle of the freezing winter, and government computer systems could be crippled. The objective of such hacking would be to demoralize the Ukrainian people and cause them to lose confidence in their government

GPS Jamming, Spoofing.

Another avenue of attack is to interfere with Ukraine's access to the Global Positioning System, or GPS. Russia has the ability to jam or spoof GPS. The former prevents users from receiving GPS data, while the latter causes users to receive false or misleading GPS data. This could make coordination between Ukrainian military units more difficult and further demoralize the population. Russia uses its own positioning, navigation, and timing satellites (known as GLONASS), so the Russian people would be unaffected by meddling with the competing system.

Attack Submarine Sorties.

Direct U.S. and NATO intervention on the side of Ukraine is unlikely, but within the realm of possibility (Ukraine is not a member of NATO). One precautionary measure Russia might take would be to sortie as many attack submarines into the North Atlantic as possible in the days before a conflict begins. Submarines such as the Russian Navy's new Yasen cruise missile submarines could launch a swarm of attack cruise missiles, the low-flying missiles taking shorter and less predictable routes to targets in the British Isles, Scandinavia, and Western Europe.

In the event that the U.S. begins shipping equipment from North America to Ukraine by sea, those same submarines could attack slow-moving convoys laden with military vehicles and supplies, just as the German Navy did during World War I and World War II.