Sony is well known for launching several smartphones a year. It doesn't stick to the annual refresh cycle that many of its competitors do, instead it opts for more of a bi-annual cycle with both its flagship and mid-range series of devices.

The latest smartphone to join the Sony Mobile portfolio is the successor to the Xperia M4 Aqua that was announced at Mobile World Congress at the beginning of March.

Just five months on we have been greeted with the Xperia Z5, dropping the Aqua name but keeping the waterproofing. We have crunched the numbers and compared the specs to see how things have changed and what the differences are between the Xperia M4 Aqua and the Xperia M5.

The Xperia M5 is only just smaller than the Xperia M4 Aqua, but it is both thicker and heavier. The new device measures 145 x 72 x 7.6mm and the dual-SIM model hits the scales at 142.6g.

Its predecessor measures 145.5 x 72.6 x 7.3mm and weighs just 136g so there isn't much in it in terms of size, but the new model adds a couple of grams to the weight.

The M5 will be available in black, white and gold, while the M4 Aqua is available in black, white and coral.

We loved the design of the Xperia M4 Aqua and the Xperia Z5 appears to follow a similar look, replicating the flagship Z series. Both the M4 Aqua and the M5 are IP65 and IP68 rated and both feature capless Micro-USB ports.

The Xperia M4 Aqua and the Xperia M5 both feature 5-inch displays but the Xperia M5 has increased the resolution.

The M4 Aqua features a 1280 x 720 resolution display, which delivers a pixel density of 294ppi. The Xperia M5 increases this to Full HD 1920 x 1080, which means more pixels per inch at 440ppi. This should offer sharper, crisper images.

The display on the M4 Aqua was sufficient. It didn't offer a great deal of vibrancy with its colours and whites were a little dim. There was also some fuzz on the top bar where the battery and time are displayed, but we suspect the bump in resolution will help improve the screen experience.

The main difference in these two devices is the cameras. The Xperia M4 Aqua features a 13-megapixel rear camera and a 5-megapixel front snapper but the Xperia M5 jumps these up to 21.5-megapixels and 13-megapixels, respectively.

The new device will be capable of 4K video recording from the rear snapper, while the M4 Aqua could only handle 1080p. The front camera on the M5 will be able to record 1080p video, while the front camera on the M4 Aqua was only 720p so there has been an improvement here too. Additionally, Sony has introduced 5x clear image zoom on the M5, taking over from the 4x digital zoom of the M4 Aqua and you'll also get Hybrid AF on the new device.

Video stabilisation and image stabilisation are on board both devices, but the M5 will also offer auto scene recognition whereas the M4 Aqua did not. The camera on the M4 Aqua was one of its biggest downfalls so we'd hope for a big improvement with the M5.

The Xperia M5 has an octa-core 64-bit processor under its hood, but it moves from Qualcomm to MediaTek and ups the speed from 1.5GHz found within the M4 Aqua to 2GHz. There is also an increase in RAM from 2GB to 3GB, which should mean the new device will be more capable of handling harder tasks.

In terms of storage, the M5 will come with 16GB internal memory, which means Sony has chosen to ditch the option of an 8GB model, which users could get with the M4 Aqua. Both come with microSD support for storage expansion up to 200GB so there isn't much change in terms of storage.

The battery capacity has seen a slight increase with the new model however, jumping up fro 2400mAh to 2600mAh, but with the display resolution jump, we suspect the running time will be around the same, with perhaps a slight improvement on the M5.

The Sony Xperia M4 Aqua and Xperia M5 both run on Android Lollipop with Sony's overlay on top.

This means you'll get a very similar software experience with both but as these are both mid-range devices, you won't get features such as PS4 Remote Play, as you do with Sony's flagship Z series.

Sony's Walkman and entertainment apps will be on board though, along with the Xperia Lounge app. You'd notice a slight difference between the M series and the Z series, but not between the two M series devices.

The Sony Xperia M5 makes improvements in most areas over the Xperia M4 Aqua, as you would expect from a succeeding device.

It may be a fraction of a millimetre thicker and a few grams heavier, but the M5 offers a sharper display, bigger battery capacity, faster processor and the potential for big camera improvements.

Pricing details haven't been announced yet but if Sony makes the Xperia M5 around the £200 mark like the Xperia M4 Aqua, it might even have the new Moto G shaking in its boots.