The frequency you have pointed out is part of the HF-GCS system. It can be heard world wide by design. Very often the same message is broadcast at the same time on all primary HF-GCS freqs. You might try, in addition to 6739 kHz, the frequencies of 4724, 8992, 11175, 13200, and 15016 kHz. All in USB mode. 11175 kHz generally yields the most interesting traffic of the bunch. If propagation is making one frequency weak or noisy for you trying another may yield a better signal.
For reference, you might want to use a thread title a bit more descriptive, maybe include the frequency and type of traffic in your title, say “6739 kHz US military traffic” or “6739 HFGCS”, something like that. It makes it easier to track threads. Also, when posting, it is most common to give the time and date you hear something as well as the frequency and mode. For radio applications time is given almost universally in GMT.
So, when possible, a post about an intercept should contain date, time (both date and time in GMT), frequency, and mode. This gives others the most probability of either identifying your reception or possibly even tuning in and finding it themselves.