The Race2Recovery team is trying to complete the Dakar Rally to raise funds for Help for Heros.
The charity is raising funds for the Tedworth House recovery and rehabilitation centre in Wiltshire.
The two US Marines involved with the race are also raising funds for the Heros Project which supports injured service men and women in America.
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Pictures on social media showed the vehicle beside the postbox lying on the ground in the tennis star’s hometown of Dunblane.
Temperatures are likely to peak at around 37C across parts of the south east on Thursday - threatening both July and UK all time records.
The Culture Secretary says the UK is still seeking clarity on the implications of the US’s ban on Huawei trading with American companies.