The impending invasion of the Soviet Union required the movement of German air power to the East, and the Blitz ended in May 1941.

We all know the horror of the events of D-Day, when the invasion required only transport across the English Channel.

The chiefs have said that an invasion would require at least 200,000 troops and have expressed deep concerns that Mr. Hussein might use biological or chemical weapons.

The invasion did require a large army build-up like the 1991 Gulf War, but many did not see combat and many were withdrawn after the invasion ended.

An invasion of North Vietnam would have required huge further investments of lives and money, and run what then were thought to be high risks of war with China and/or the Soviet Union.

The invasion of a central naval port in itself however, does not guarantee the surrender of a naval power, and may require the entire surrounding region to be occupied before starting the invasion.

"They realized our Achilles heel was logistics," said a high-ranking officer, meaning that a large-scale invasion requires an influx of trucks and equipment to travel Iraqi roads.

The most recent invasion had required Federation intercession.

An invasion from the north would require the patience destruction of the line of fortifications and water obstacles that the Spaniards had constructed opposite the equivalent Dutch defensive belt.

It was also estimated that an invasion of Formosa would require about 12 divisions of US Army soldiers and Marines.