The battle to win same-day delivery has raged for years, but Amazon has remained a relatively quiet player—until now.

Today, the company unveiled free same-day delivery for members of its wildly popular Prime service in 14 US metro areas. The new service is a more limited version of Prime’s trademark free two-day shipping. A mere 1 million items are available for same-day delivery, as opposed to the 20 million eligible for standard-issue Prime. To qualify for the perks, orders must be placed before noon and total at least $35.

While Amazon has offered experimental versions of same-day delivery for years, it's waited to offer such a service widely until it had built up its logistics infrastructure to make same-day scale. The company has spent massive amounts of money over the past several years to build huge fulfillment centers near major metro areas. That spending took a huge chunk out of the company’s bottom line—but the gamble was that the speed it would gain to allow for same-day deliveries would put it way ahead of both its online and offline competitors.

The question for Amazon, however, is whether it’s really figured out how to make same-day delivery pay.

Now, assuming the service works, Amazon appears to be well ahead of rivals both large and small. Both Google and eBay have taken stabs at same-day delivery, but neither has a physical infrastructure for handling inventory at scale, relying instead on local chain stores to fulfill orders. Walmart has also experimented with same-day, but it remains a primarily brick-and-mortar business.

The question for Amazon, however, is whether it's really figured out how to make same-day delivery pay. Last December, the company rolled out a smaller service, called Prime Now, which delivered 25,000 “daily essentials” to a Prime customer’s door within an hour for a $7.99 fee. Prime Fresh, meanwhile, offered same-day delivery for groceries, but for a much higher annual membership fee. These extra fees likely didn’t make sense for cost-conscious consumers if waiting a couple more days would make the package free. They also reflected the apparent extra cost to Amazon of speeding up delivery.

By offering same-day for free, Amazon looks to be relying on the same growth-before-profits strategy that has led to the massive growth of its core retail business. By making same-day free, many more customers will likely give same-day a try. If it becomes popular, consumers may come to expect that same level of service at the same price from everyone else—and everyone else will be hard-pressed to match it. If Amazon’s same-day scheme succeeds, it will combine the best of brick and mortar (getting it right now), with the best of e-commerce (huge selection and low price). After all, Amazon doesn't want to dominate just online retail. It wants to own retail, period.