British police officers are not routinely armed. Instead, they rely on specially trained Authorised Firearms Officers (AFO) to attend incidents where firearms might be needed. Specialist Firearms Officers are usually trained to a higher standard than an AFO, because they are likely to be the officers required to enter besieged premises. The vast majority of firearms used by the British Police are semi-automatic. Police use of force regarding firearms is governed by the Association of Chief Police Officers (ACPO).