A severe U.S. weakness. Here's What You Need to Remember: As plans for a more advanced KC-Y tanker have been shelved, there could be additional orders for more Pegasuses as more KC-135s age out in coming decades. If this comes to pass, the new tankers may remain active through the end of the twenty-first century. In 2018 the Air Force plans to bring its first eighteen KC-46A refueling tankers into service—paving the way for the replacements of its vast fleet of KC-135 Stratotankers that date back to the 1950s. The Pegasus should prove significantly more efficient and survivable than its predecessor, but its final rounds of testing have been bedeviled by a few persistent bugs.