There have been attempts to produce a military strength index: this is an example taken from a Credit Suisse report in September 2015. The factors under consideration for that military strength indicator and their total weights were: number of active personnel in the army (5%), tanks (10%), attack helicopters (15%), aircraft (20%), aircraft carriers (25%), and submarines (25%). It was practically impossible to make an estimation of the actual training of the armed forces.  These were the results:
For those who are interested in enlisting in the military, they are screened using the Armed Forces Qualification Test (AFQT), which is comprised of a subset of scores from the ASVAB. Successfully passing the AFQT is not the sole requirement for enlisting but is one of the qualifications that must be met. There are various requirements for the different branches of the military and those interested are encouraged to contact recruiters to obtain more information about requirements specific to that branch.
A major development in infantry tactics came with the increased use of trench warfare in the 19th and 20th centuries. This was mainly employed in World War I in the Gallipoli campaign, and the Western Front. Trench warfare often turned to a stalemate, only broken by a large loss of life, because, in order to attack an enemy entrenchment, soldiers had to run through an exposed 'no man's land' under heavy fire from their opposing entrenched enemy.
As of 2017, the U.S. spends about US$610 billion annually to fund its military forces and Overseas Contingency Operations. Put together, the U.S. constitutes roughly 40 percent of the world's military expenditures. The U.S. Armed Forces has significant capabilities in both defense and power projection due to its large budget, resulting in advanced and powerful technologies which enables a widespread deployment of the force around the world, including around 800 military bases outside the United States. The U.S. Air Force is the world's largest air force, the U.S. Navy is the world's largest navy by tonnage, and the U.S. Navy and the U.S. Marine Corps combined are the world's second largest air arm. In terms of size, the U.S. Coast Guard is the world's 12th largest naval force. 
High school students can take the test in their sophomore, junior, or senior years, although scores from sophomore tests can’t be used for enlistment purposes. There is no charge to sit for the exam, and the results will have no impact on your high school academic record or your college application. This is a risk-free way to better evaluate your opportunities for the future after high school graduation.
Figure out which areas to focus on based on your career goals. If you’re not interested in a job requiring a score on the Mechanical Comprehension subtest, you don’t need to worry about doing well on that subtest. If you don’t need to worry about mechanics, don’t bother preparing for that section. Spend the time on Word Knowledge or Arithmetic Reasoning.
Additionally, all services except for the Air Force have an active warrant officer corps. Above the rank of warrant Officer One, these officers may also be commissioned, but usually serve in a more technical and specialized role within units. More recently, they can also serve in more traditional leadership roles associated with the more recognizable officer corps. With one notable exception (Army helicopter and fixed-wing pilots), these officers ordinarily have already been in the military often serving in senior NCO positions in the field in which they later serve as a warrant officer as a technical expert. Most Army pilots have served some enlisted time. It is also possible to enlist, complete basic training, go directly to the Warrant Officer Candidate School at Fort Rucker, Alabama and then on to flight school.
The Armed Forces Qualification Test (AFQT) derives from the more comprehensive, 10-subtest Armed Services Vocational Aptitude Battery (ASVAB). Scores on the four ASVAB math and verbal subtests are used to calculate an AFQT score, which determines whether an individual is generally qualified to enlist. Performance on all 10 ASVAB subtests, meanwhile, ascertains an enlistee's qualifications for specialized work within the military and possible incentives for enlistment.
The Armed Forces Qualification Test (AFQT) is used by all of the Services to determine if an applicant is eligible for the military. Four of the ASVAB subtests are combined to form the AFQT. It measures general cognitive ability and is composed of verbal and mathematics subtests. AFQT scores are grouped into categories for reporting purposes. The table below shows the AFQT categories and the percentile score ranges corresponding to the categories. Applicants that score in AFQT category IIIA or higher may qualify for enlistment incentives.