The troops were preparing for Tuesday's State Procession that will mark 60 years of Queen Elizabeth II's reign, The Daily Telegraph reported.
The King's Troop Royal Horse Artillery simulated firing a 60-gun salute.
The 1902 state carriage that will transport the queen and duke of Edinburgh from a thanksgiving service Tuesday at St. Paul's Cathedral followed the mounted regiment but was empty for the rehearsal.
Other carriages from the Royal Mews, which will carry other members of the royal family, also participated in the rehearsal.
In contrast to the thousands of people expected for Tuesday's procession, only a few joggers were the audience for the rehearsal.
Warrant Officer 1 Paul Barker, state ceremonial training officer for the Royal Navy, said he was pleased with the rehearsal.
"It went very well this morning. We are at the right stage that we need to be at. We don't want to peak too early but it's everything I expected them to achieve," Barker said.
"On Tuesday, there will be a mixture of nerves and pride; this is a one-off event, it's not going to happen again in our lifetime and it will give us lots and lots of memories for the future."