Oshkosh Corp. (OSK) on Tuesday reported a nearly 20% drop in fourth-quarter sales and a $1 billion loss for the year, but said its quarterly profit more than doubled as the result of strong military vehicle orders.The company had $1.5 billion in sales in the three-month period that ended Sept. 30, compared with more than $1.8 billion in the same period a year ago.Military-vehicle sales were up 55%, to $855 million, as Oshkosh Corp. received long-term government contracts worth billions of dollars.