The Sirens Women’s Motorcycle Club is New York’s oldest and largest all-women motorcyclists’ club. But its members aren’t exactly badass bikers.

They currently work with the New York Milk Bank (NYMB), a bank which collects, pasteurises and delivers breast milk to babies or hospitals in need. Pasteurised donated milk is crucial for babies, especially those who are ill or premature, whose mothers may be unable to produce enough milk.

NYMB opened in September, 2016, founded by Julie Bouchet-Horwitz, a nurse practitioner and lactation consultant, and has already delivered more than 30,000 ounces of milk to babies in and around New York. Usually, the bank uses mail or delivery services like Fed Ex for their deliveries, but with the heavy traffic in New York City, deliveries are a challenge. “I was stuck in traffic one day and saw a motorcycle weaving in and out,” Bouchet-Horwitz told Fox News. “That’s when I thought, ‘Why can’t we use a motorcycle rider to deliver milk through Manhattan?’” And so she founded the Sirens Motorcycle Club, who are now on call at all times, even late at night.

Founded in 1986, the goal of the motorcycle club is to carve out a space for women in a male-dominated culture of motorcycling. “We are women motorcyclists first. Any woman, any bike,” said Jen Baquial, president of the club. “We are a small group of women, but we all know that every little bit counts,” she said to HuffPost, adding, “Riding our motorcycles together gives us immense joy, but doing service in the community together gives us purpose.” Their community service includes helping homeless girls, addressing breast cancer, and participating in the LGBT Pride March every year.