The phrase 'double the strength' is correct and can be used in written English.
You can use it when referring to making something stronger or increasing something's power or effectiveness. For example: We need to double the strength of our security measures to protect our network.
Mr. Karzai said that if he was re-elected, his priority would be bringing peace and security to the country; he promised to double the strength of the Afghan police and army forces by the end of his second elected term.
Midair collisions of sand particles can double the strength of a sandstorm, according to new computer simulations.
Between 2012 and last year, it underwent a $94 million upgrade to double the strength of the its main magnetic field and add a second port to inject neutral atoms to heat the plasma, which can reach temperatures above 15,000,000°C, hotter than the sun.
It was concluded that placing the openings near the upper corners of the deep beam may double the strength, and the use of a rectangular narrow opening, with the long sides in the horizontal save up to 40%% of structural strength of the deep beam.
However, the Imperial reaction to these attacks was to double the strength of their forces.
Indeed, in 1938 the government decided to double the strength of the Militia as war clouds began to loom on the horizon, and late in the year a recruiting campaign was launched that saw the size of the Militia increase from 35,000 to 43,000 men over the space of three months.
The deal had doubled the strength of Hamas, Livni said in an interview with Yedioth Ahronoth, Israel's biggest-selling daily.
That strategy has the effect of doubling the strength of the electric field between the eel's positive pole (which is located near the head) and its negative pole (which is located near the tail).
To match the American machine, however, the Europeans, with a much smaller tunnel — 17 miles instead of 54 —had to adopt a riskier design, in particular by doubling the strength of their magnets.
Including midair collisions in the model increased the flux, in extreme cases approximately doubling the strength of the storm, they report online this month in Physical Review Letters.
The Second Regiment of the First Imperial Guards had entered the palace grounds, doubling the strength of the battalion already stationed there, presumably to provide extra protection against Hatanaka's rebellion.
