对一个英文句子的疑惑,求解答."McDowell hopes all visitors to New York will

对一个英文句子的疑惑,求解答.
"McDowell hopes all visitors to New York will feel safer when they see the USS New York keeping watch in the city's harbor,as a symbol of strength and national resolve."中的“ keeping watch”有没有问题?正常情况keep应该后面跟动词ing形式才对,例如：keep watching...这里为什么就可以用“keeping watch”呢?