Strikebreakers (called "scabs") were threatened and sometimes attacked. This is sometimes accomplished by the importation of replacement workers, strikebreakers or "scabs". The major meatpacking plants hired blacks as strikebreakers in 1917. It was also used by union strikers to describe poor white strikebreakers. On December 1, 1919, the striking dockworkers rushed the harbour and chased off the strikebreakers. Four striking workers were killed when strikebreakers protected by police fired into a crowd. However, union miners killed 20 men of the 50 strikebreakers and mine guards who surrendered. As industries hired blacks as strikebreakers in some cities, worker resentment against them increased. The railroads began hiring replacement workers (strikebreakers), which increased hostilities. The railroads simply hired replacements, among them African-American strikebreakers, and withstood diminishing union pressure. In some cases, unions' strike have led to violent clashes with police and with strikebreakers. South Omaha's working-class whites showed great hostility toward black strikebreakers. The title song was unusually aggressive in its language towards the strikebreakers. Navy personnel were also used as strikebreakers in the oil industry. Many of the strikebreakers were students at Harvard University.