In the beginning, all Packards had a single-cylinder engine until 1903. The first Packard 4-cylinder engine was introduced as the Model K in 1903, and the first six-cylinder engine was introduced as the Series 1-48 Six in 1912. Packard produced its "Twin Six" model series of 12-cylinder cars from 1915 to 1923. The Packard Eight was introduced in 1930 and the V8 appeared in 1955, one year after Buick and a few decades after Cadillac and Lincoln. All Packard engines were flathead engines until the last few years before the company ceased operations. Packard vehicles featured innovations, including the modern steering wheel, air-conditioning in a passenger car, and one of the first production 12-cylinder engines, adapted from developing the Liberty L-12 used during World War I.