CAMM is Short to medium range anti-aircraft and anti-missile missile. CAMM (Common Anti-Air Modular Missile) series is a family of surface-to-air missiles developed by MBDA for the United Kingdom.

From Wikipedia

CAMM shares some common features and components with the ASRAAM air-to-air missile, but with updated electronics and an active radar homing seeker. The Common Anti-Air Modular Missile is intended to replace the Sea Wolf missile on Type 23 frigates of the Royal Navy from 2017, the Rapier missile in British Army service from 2018 and is contributing to the updating of MBDA's ASRAAM in service with the Royal Air Force.

CAMM is a point defence and local area defence missile designed to respond to sophisticated missile attacks and has the capability to defend against saturation attacks of supersonic anti-ship cruise missiles, aircraft and other high-performance targets. It does this via multiple channels of fire, providing 360-degree simultaneous coverage and high degrees of manoeuvrability. MBDA state that CAMM has a "high rate of fire against multiple simultaneous targets", providing capabilities comparable to the Aster 15 missile.

Design characteristics allow for low cost by modularity and minimising electromechanical complexity through implementing most functionality in software. Additionally, the command and control software reuses over 75% of that developed for the PAAMS system.

CAMM has a minimum operational range of less than 1 km and a maximum range greater than 25 km, although IHS Jane's reports that trials have a shown a capability of up to 60 km. These ranges are significantly greater than the 1–10 km range of Sea Wolf and other systems CAMM will replace. CAMM is 99 kilograms (218 lb) in weight, 3.2 metres (10 ft) in length, 166 millimetres (6.5 in) diameter and reaches generous supersonic speeds of Mach 3 (or 1,020 meters per second).

CAMM's claimed benefits include:

Active, next-generation RF seeker that provides true all-weather performance with excellent clutter rejection capabilities and means there is no need for complex and high-cost fire control/illumination radars

A two-way datalink providing outstanding accuracy and highly improved functionality. The associated radar system tracks the threat and uses the datalink to update the missile with the location of the threat before the seeker takes over the missile guidance.

A Soft Vertical Launch (SVL) system that offers 360° degree coverage and high degrees of manoeuvrability. CAMM also uses a gas generator to eject the missile from its canister, the benefits of which include increased range – by saving all the rocket motor's energy to power the intercept – reduced minimum intercept range, reduced stress on launch platforms, significantly reduced maintenance costs, more compact installations on ships and there being no need to manage the hot gas efflux on board, reduced launch signature, and on land the possibility of firing the missile from wooded or urban areas.

CAMM comes in its own launch canisters, or alternately can be quad-packed into the SYLVER, ExLS and Mark 41 vertical launching systems found on many warships.

CAMM's Extended Range application is known as CAMM-ER and has been under development with MBDA for the Italian MoD since 2013[26]. The CAMM-ER (extended range variant) shares the same characteristics of the original CAMM with the exception of an additional rocket booster which significantly increases the missile's engagement range, out to 45 km and a slightly adapted missile structure. The missile is 160 kilograms (350 lb) in weight, 4.2 metres (14 ft) in length, 190 millimetres (7.5 in) diameter.

Royal Navy's new Sea Ceptor missiles in action | MBDA CAMM (Common Anti-Air Modular Missile)

Sea
The maritime application of CAMM is known as Sea Ceptor. The system will provide the principal air defence capability for the Royal Navy's Type 23 and Type 26 Frigates, as well as arming other navies around the world. Sea Ceptor can be easily retrofitted onto a wide range of platforms, from 50m OPVs to frigates and destroyers.

In addition, CAMM can also be integrated with a range of radar types to suit customer requirements. MBDA claim that CAMM has a "wide target set", including the capability to engage small naval vessels, which would give the missile a limited surface-to-surface role.[24 This has since been confirmed by the Royal Navy, with the Anti-Air-Warfare Officer of Type 23 Frigate HMS Westminster stating: “Westminster managed to explore the real potential of the system during her training and to say it is a real game changer is an understatement. Unlike its predecessor, the system is capable of defending ships other than Westminster herself. Whether it’s engaging multiple air threats or fast incoming attack craft, Sea Ceptor represents a massive capability upgrade for the Type 23 frigate.”

Land
On the land domain, CAMM is known as Sky Sabre by the British Army. This application has over three-times the range of its predecessor Rapier, it is able to intercept the most challenging targets in all-weather conditions

For international customers in the land domain, MBDA markets the Enhanced Modular Air Defence Solutions (EMADS). This is a rapidly deployable point and area defence system designed to protect mobile and static high value assets. It provides all-weather protection against a spectrum of conventional and challenging air targets, including low level terrain and high altitude threats. Each EMADS launcher is scalable and can carry multiple CAMM or CAMM-ER missiles as well as being highly mobile with excellent off-road capability. The system provides EMADS with pre-launch targeting information based on track data from a suitable radar sensor.

Air
Originally, the CAMM program aspired to provide Land, Sea and Air launched capabilities, but it was deemed more effective to instead develop CAMM for use in the Land and Sea domains, while using the well established and highly capable ASRAAM short range air-to-air dogfighting missile to cover the Air Launched domain. However, technologies and components developed for CAMM have been leveraged as part of an upgrade to ASRAAM.

So there are the specs and information about the missile, was there a better option for the navy? Yes there ESSM the upgraded version of the Sea Sparrow (RIM-162 Evolved SeaSparrow Missile). ESSM has a better range, larger warhead. and would have fit in the Mk 41 VLS (which the RNZN frigates had) To make ESSM effective we would have had to upgrade the radar suite (which we kind of are anyway) but would require more than the on lumination radar, to something like CEFAR or Aegis system to handle multiple luminations at once

But CAMM doesn't really require a new tracking or lumination radar as once a target is identified CAMM is self-guiding to target.  CAMM is lighter that ESSM as well which was an issue with the NZ frigates with top weight. And should be able to fit in with any CMS like the Lockheed Martin CMS 330.

So our allies like Australia, Canada, US and many others, choose ESSM over CAMM which means commonality between allies, or in the time of need, if we require parts or require more missiles then our allies could help out. But since we choose CAMM then our closest ally is the UK on the other side of the planet. Although Chile and Brazilian have also chosen CAMM they are not exactly allies.