Numerous airlines fly from Heathrow to Austrailia, from different terminals.
Delta uses Heathrow terminal T4.
west 2 east
You may not have the choice, only certain airlines fly in to Gatwick.
Delta fly in and out of Terminal 4 at London Heathrow. See related link for more information.
Zoom Airlines from Gatwick and Stansted British Airways and Air Canada from Heathrow Air Transat from Gatwick
3hr 40min to 4hr 05min London Heathrow (LHR) to Moscow Domodedovo (DME) or Moscow (SVO) by a nonstop flight operated by BMI - British Midland Airways, Aeroflot - Russian Airlines, British Airways or Transaero Airlines.
9hr 10min to 9hr 40min Delhi (DEL) to London Heathrow (LHR) by a nonstop flight operated by British Airways, Jet Airways or Virgin Atlantic.
Kenya Airlines fly scheduled flights from London Heathrow (LHR), which is a short car journey from Reading (approx 30 mins).
There are no flights which fly directly from Heathrow to San Antonio, the nearest to San Antonio which has flight access from Heathrow is Houston George Buch Intercontinental Airport. There are two United Airlines and two British Airways flights from Heathrow per day.
T4.
There are many flights to Seattle to Heathrow. There are many airlines that has flights to Seattle from Heathrow. Some airlines that has flights to Seattle from Heathrow are One2One, British Airways, Travel Up, and ComeFli.